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Recent problems solved by 'jrfrunner'
jrfrunner answered: 364 problems
Jump to solutions: 0..29 , 30..59 , 60..89 , 90..119 , 120..149 , 150..179 , 180..209 , 210..239 , 240..269 , 270..299 , 300..329 , 330..359 , 360..389, >>NextTriangles/333575: the flower garden has the shape of a right triangle. 5 ft of a perrineal border forms the hypotenuse of the triangle and one leg is 1 ft longer than the other legs, find the lengths of the legs
Can you please help me thank you 1 solutions
Answer 239064 by jrfrunner(365) on 2010-08-21 16:41:55 (Show Source):
You can put this solution on YOUR website!When you are dealing with a right triangle and you are trying to find lenght of the sides, you will most likely end up using the pythagorean theorem which states:  where c is the side opposite the right angle, and is called the hypotenuse.
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Given in your problem: c=5, a=x and b=x+1
so by the pythagorean theorem of a right triangle: 
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 (expanding the squared term)
 (combining terms)
 (putting the quadratic equation in standard form}}}
 (divide the whole thing by 2, to simplify the equation)
0=(x+4)*(x-3) (factor the expression on the right)
x=-4, x=3, since we are dealing with lengths, the negative value x= -4 is extraneous and can be trown out
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so, one side is a=x=3 and the other is b=x+1=4
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what you have is a special type of right triangle where the sides are in a ratio 3:4:5
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Travel_Word_Problems/333545: Jason and Kim were at the park. If they both left at the same time, and Jason was driving at 30 mph, and kim was driving at 40 mph in the opposite direction, how long will it be before they are 210 miles apart? 1 solutions
Answer 239061 by jrfrunner(365) on 2010-08-21 16:27:35 (Show Source):
You can put this solution on YOUR website!You need to understand the relationship:
d=r*t (distance = rate*time)
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Kim's distance after t hours: 
Jason's distance after t hours: 
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They are travelling in opposite directions and you need to know the time when they are 210 miles apart, so add their distances
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210/70 =t
===
t = 3 hours
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Miscellaneous_Word_Problems/333627: Bill swims at a speed of 6.7 mph in still water. The river he's in flows at a at speed of 3.6 mph. How long will it take Bill to swim 1.3 mi upstream?Round your
answer to the nearest tenth of an hour, if necessary.
1 solutions
Answer 239058 by jrfrunner(365) on 2010-08-21 16:06:41 (Show Source):
You can put this solution on YOUR website!Bill swims at a speed of 6.7 mph in still water. The river he's in flows at a at speed of 3.6 mph. How long will it take Bill to swim 1.3 mi upstream?
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You need to understand the relationship:
d=r*t (distance = rate*time)
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Since you need to find time,rework this formula to find time (t=d/r)
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you are given the distance d = 1.3 miles
The speed is the "net speed" he travels during this distance.
Since he is swimming upstream, he is fighting the river flow
Therefore, his net speed is his speed in still water minus the river flow
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net speed: (Bill's speed - river flow)==> r = 6.7mph - 3.6 mph = 3.1 mph
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time to swim 1.3 miles: t = d/r =1.3 miles /3.1 mph = 0.419 hours or 0.4 hour rounded to nearest tenth of an hour
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Exponents/333459: A school has a telephone system for letting parents know about emergency school closing. The system is a pyramid with five layers. Three parents are on top layer of the pyramid. Each parent in each layer calls three different parents. How many parents are in the chain? 1 solutions
Answer 238971 by jrfrunner(365) on 2010-08-20 22:52:06 (Show Source):
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Problems-with-consecutive-odd-even-integers/333482: The product of two consecutive integers is 4 less than four times their sum. Find the integers.I had tried to solve it but it made me just get more confused with the whole question. 1 solutions
Answer 238959 by jrfrunner(365) on 2010-08-20 20:35:46 (Show Source):
You can put this solution on YOUR website!A. two consecutive integers : x and x+1
B. The product of two consecutive integers x*(x+1)
C. 4 less than four times their sum: 4[x+(x+1)]-4
D. x*(x+1)=4[x+(x+1)]-4 (equate the sides)
E. x^2+x=4(2x+1)-4 (simplify the equation)
F. x^2 +x=8x+4-4=8x (simplify the equation)
G. x^2=-x+8x=7x (subtract x from both sides)
H. x=7 (divide both sides by x)
===
check solution by substituting x=7 back in original equation
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x*(x+1)=4[x+(x+1)]-4
7*(7+1)=4*(7+(7+1))-4
7*8=4*(15)-4
56=60-4=56
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Probability-and-statistics/333313: 2. A scientist wants to compare two delicate weighing instruments by repeated weighing of the same object. The first scale is used 30 times and the weights have a standard deviation of 72 milligrams. The second scale is used 41 times and the weights have a standard deviation of 98 milligrams. At the 0.05 significance level, test the claim that the second scale produces greater variance. 1 solutions
Answer 238930 by jrfrunner(365) on 2010-08-20 16:17:47 (Show Source):
You can put this solution on YOUR website!To test the hypothesis of two variances use the F distribution and a test statistic F= 
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Ho: 
Ha:
at 
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critical value: 
test statistic 
--
reject Ho if test statistic > critical value
since test statistic = 1.853 > critical value=1.806 then reject Ho
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conclusion:
at the  level, the evidence suggest that
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Miscellaneous_Word_Problems/333406: Give an example of something having these distribution shapes: (a) bimodal,
(b) approximately rectangular, and (c) positively skewed 1 solutions
Answer 238929 by jrfrunner(365) on 2010-08-20 16:03:00 (Show Source):
You can put this solution on YOUR website!(a) bimodal
This is usually a mixture of two different distribution, such as heigths of people, there is the distribution for men and for women, so if we dont separate the genders, there will tend to be a bimodal effect
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(b) approximately rectangular
This is the uniform distribution, where all events have equal probability of occuring. Such as tossing a die, the probability of 1 or 2, 3 etc each has 1/6 chance of occuring
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c) positively skewed
Many distributions are positively skewed (have long tails to the right)
examples are wealth distributons (a few people have the largest amounts of money)
population by country, some countries have most of the populations
country sizxe, a few countries have the biggest square aress,
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Probability-and-statistics/333394: Consider the following statements:
A. The salary of an employee at the hotel is a nominal variable.
B. The distance travelled by motor on a freeway is an interval variable.
C. The outcome of a soccer match is an ordinal variable.
D. Degree obtained at a university is a nominal variable.
Which of the following statements is / are correct?
1. Only A
2. A and C
3. Only C
4. B and D
5. Only D 1 solutions
Answer 238928 by jrfrunner(365) on 2010-08-20 15:52:12 (Show Source):
You can put this solution on YOUR website!Nomimal means a label or category that has no order
Ordinal means a ranking, rating, its not measured on a continuous scale but has order
Interval means it can be measured in a continous scale
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B & D would b e the logical answers
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Permutations/333411: find the number of ways in which an arrangement of of 4 letters can be made from the word MATHEMATICS
a)1680
b)756
c)18
d)2454 1 solutions
Answer 238927 by jrfrunner(365) on 2010-08-20 15:46:51 (Show Source):
You can put this solution on YOUR website!while the word MATHEMATICS has 11 words, there are really only 8 unique words
M, A and T are duplicated.
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So, your problem becomes number of arrangements of 4 letters from a word of 8 unique letters
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there are 8 choices for the first word
there are then 7 choices for the second word
after that there are 6 choices for the third word
and finally there are 5 choices for the fourth word
8*7*6*5=1680
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Triangles/333416: if i have the measurements of a video screen that is 17.5 ft diagonally, how can i figure out the height and width of this video screen? 1 solutions
Answer 238925 by jrfrunner(365) on 2010-08-20 15:40:56 (Show Source):
You can put this solution on YOUR website!unless the video screen is a square, there is not enough information to figure out the length and width. You need to provide either a ratio of L to W or the angle that the diagonal makes to one of the sides.
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Age_Word_Problems/333422: For the problem I have to solve it says I have to write a system of equations involving two equations in two variables then to solve the system. Here is the problem: Jean is twice as old as Michael. The sum of their ages 3 years ago was 45 years. Find their ages now.
I tried to solve it without the sytem of equations and i got the answer of jean:32 and Michael:16 but then I realized I would get the question wrong if I didn't show the system of equations. Please help me. 1 solutions
Answer 238919 by jrfrunner(365) on 2010-08-20 15:27:34 (Show Source):
You can put this solution on YOUR website!first, your answers, of Jean=32 and Michael 16, have you tested them to see if they are correct? The sum of their ages 3 years ago was 45 years
Let see, 3 years ago Jean=32-3=29, Michael=16-3=13 so their sum is 42, so your answers are incorrect!
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Begin by letting J=Jean's age and M=Michaels age, you have two unknowns J and M
and you need as many equations as unknowns.
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Jean is twice as old as Michael
J=2*M [ this is your first equation ]
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The sum of their ages 3 years ago was 45 years
J-3 is jean's age 3 years ago
M-3 is Michaels age 3 years ago, so....
(J-3) + (M-3)=45 [ this is your second equation]
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simplify the second equation
(J-3) + (M-3)=45
J+M-6=45
J+M=51
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So now you have two equations and 2 unknowns
There are many ways to solve this, substittution, elimination, matrices, graphing, guessing, cramer method, etc......
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Try subtitution since the first equation is already set to one of the variables
J =2*M
substitute this into the second equation
J+M=51
(2*M)+M=51
3*M=51
M=51/3=17
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So if M=17 and J=2*M then J=2*(17) =34
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Check your answers
go back to the original equations
J=2M and (J-3) + (M-3)=45 to see if M=17 and J=34 are valid
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Miscellaneous_Word_Problems/333428: The mass of Mercury is about 3.302x10^20 metric tons. The mass of the sun is about 1.998x10^27 metric tons. About how many times the mass of Mercury is the mass of the sun? Give answer in scientific notation. 1 solutions
Answer 238915 by jrfrunner(365) on 2010-08-20 15:10:35 (Show Source):
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Probability-and-statistics/333315: 35 employees who completed two years college were asked to take basic mathematics test. The mean and standard deviation of their scores were 75.1 and 12.8 respectively. In a random sample of 50 employees who only completed high school, the mean and standard deviation of the test scores were 72.1 and 14.6 respectively. Estimate with 90% confidence the difference in mean scores between the two groups of employees. 1 solutions
Answer 238909 by jrfrunner(365) on 2010-08-20 13:28:32 (Show Source):
You can put this solution on YOUR website!Many people will make lots of assumptions to simplify a problem like this and in many cases you will get answers close enough, but you should be aware of the proper way to do things
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1. You are dealing with a test of two independent samples, with unknown population variances.
2. You did not state the underlying distribution that these samples came from, but as long as you are analyzing averages and the samples are larger than 30, you can rely on the Central limit theorem for license to utilize Normal approximations to whatever underlying distributions you started with.
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Now just because you can rely on normal approximations does not mean you can just jump into the Z normal distribution, there is the t normal distribution.
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Since the population variances are not known, this indicates that you should use a "t" distribution. Althought, the samples sufficiently large, both the t distribution and Z distribution will merge and become indistinguishable.
but...... most people believe that this happens at samples even close to 30. In fact, the two distributions do not merge close enough until the samples are in the magnitude of approximately 200 each.
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So in your case you really should stick with the t distribution.
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To do things correctly, there are two basic types of t distribution. One for when the "unknown" population variances can be assummed equal and one where the variances cannot be assumed equal. (There is a F statistic for testing this, and I carried it out and determined that the population variances can be deemed to be equal, but I am not going to cover that here)
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So the particular t test that you use is the one where you can pool the sample standard deviations (since the population variances are deemed to be equal)
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Confidence interval for population mean differences
 -/+ 
and  =pooled_variance =
t = critical t value with 0.05 tail probability and 50+35-2 =83 degrees of freedom = 1.663, NOTE: for 90% confidence you will have 5% at the tails
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plugging in your information
 =
 -/+
3.0 -/+ 5.09
(-2.09, 8.09)is the 90% confidence interval for the population mean differences
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Probability-and-statistics/333376: Numbers 1,2,3,4,5,6,7,8,9 are written on seperate cards. The cards are shuffled and the top one turned over. Let A = to an even number. B = to a number greater than 6. Which one of the following statements is incorrect?
1. The sample space is S = {1,2,3,4,5,6,7,8,9}
2. P(A) = 4/9
3. P(B) = 1/3
4. P(A and B) = 1/9
5. P(A or B) = 7/9 1 solutions
Answer 238887 by jrfrunner(365) on 2010-08-20 10:58:34 (Show Source):
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Permutations/333367: In how many ways can the word SUNDAY be arranged.
How many arrangements begin with S and do not end with Y? 1 solutions
Answer 238880 by jrfrunner(365) on 2010-08-20 10:50:53 (Show Source):
You can put this solution on YOUR website!assuming there are no duplicated letters, there are n! different ways of ordering a word with n letters
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the word SUNDAY be arranged in 6!=6*5*4*3*2=720 ways
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The are 5! ways of ordering the word SUNDAY if the first letter is rstricted to S, because only the 5 remaining ones are allowed to change.
There are 4! ways of ordering the word SUNDAY if the first letter is restricted to S "and" the last letter is restricted to Y
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Therefore, there are 5!-4! ways that the word SUNDAY can be arranged such that the first letter is S and the last letter "is not" Y
5!-4! = 120-24 =96
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Probability-and-statistics/333318: After sampling from two binomial populations, we found the following:
p = 0.48 n1 = 100 p2 = 0.052 n2 =100
if we estimate with 90% confidence the difference in population proportions, what would be the outome?
1 solutions
Answer 238879 by jrfrunner(365) on 2010-08-20 10:41:19 (Show Source):
You can put this solution on YOUR website!you can apply the binomial method directly which can be tedious and difficult
or "if" the assumptions are met, can apply a normal approximation to the binomial.
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The enable the use of the normal approximation, the following need to be met
1.  and  and  and 
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you provided p1 = 0.48 n1 = 100 p2 = 0.052 n2 =100
NOTE: not sure if your p2 is correct. Nevertheless, it looks like the requirements above are met.
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90% confidence interval for difference in the population proportions yields Z=1.645
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Upper confidence interval value: 
Lower confidence interval value: 
---
confidence interval =  to 
--
you can do the math
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Probability-and-statistics/333361: when you throw a fair dice ,what is the probability of obtaining a number which is odd ? 1 solutions
Answer 238875 by jrfrunner(365) on 2010-08-20 09:53:05 (Show Source):
You can put this solution on YOUR website!Fundamentally, probability is straight foward
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Probability = (Number of a certain type of events)/(total number of events)
The difficult part is sometimes enumarating the number in each part of that fraction.
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In your case is not bad at all to enumarate the events.
probability of obtaining a number which is odd on a fair die, there are a total of 6 events {1,2,3,4,5,6} and there are 3 odd events {1,3,5}
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so P(a number which is odd)=Number of odd events/total events = 3/6=1/2
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Probability-and-statistics/333236: Hello Can someone help me with this problem, I did try to work it but I am not sure.
Consider a binomial distribution with 13 identical trials, and a probability of success of 0.5
i. Consider a binomial distribution with 13 identical trials, and a probability of success of 0.5
i. Find the probability that x = 2 using the binomial tables
ii. Use the normal approximation to find the probability that x = 2. Show all work.
THIS IS WHAT I HAVE SO FAR I AM NOT SURE IF IT IS RIGHT BUT HERE GOES:
P(x = 2) = jpeg will not post
X-=- 2, n=13
p = 0.5
Mean =E(X) = np =13 x 0.5 = 6.5
Standard Dev. = √np (1-p) = √13 x.0.5. x 0.5 =√3.25 =1.8027
√np (1-p) = √13 x.0.5. x 0.5 =√3.25 =1.8027
Please help me that you again.
Thank you. 1 solutions
Answer 238805 by jrfrunner(365) on 2010-08-19 22:38:25 (Show Source):
You can put this solution on YOUR website!difficult to help you with binomial tables through this medium
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some binomial tables are constructed using individual probabilites and other bionamial tables are constructed using cumulative probabilities.
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typically the proportion of interest is labelled across at the top, you would be looking for p=0.5
Then under that column, you would go down looking at for an "n" or sample size value along the right hand side (for 13 in your case). Within that sample size you would see events from 0 to the n or 13 in your case. Find for n=13 and x=2, follow that across and where this meets the column value that would represent either P(X=2) or P(X<=2) depending on how your table is constructed.
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To use the normal approximation to the binomial, keep in mind that there is an assumption that np>10, which is not met in your case, but ignoring this, though you shouldnt, then you would compute the mean and standard deviation, just like you did.
Then you would convert The X variable to a Z variable via
So you need P(X=2),
problem is the binomial (count of successes) is a discrete distribution and the normal distribution is a continuous distribution. soo .. what do you ?
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instead of P(X=2) you actually want to find P(1.5<=x<=2.5)
when you convert x to z you then have

this simplies to 
--
and from there you need to use standard normal tables, excel, statistical calculator, manual integration or some method to find this probability.
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Probability-and-statistics/333173: three balls are randomly selected without replacement from a bag containing 20 balls numbered 1, 2 through 20. if we bet that at least one of the balls has a number greater than or equal to 17 what is the propability that we will win the bet 1 solutions
Answer 238701 by jrfrunner(365) on 2010-08-19 16:39:12 (Show Source):
You can put this solution on YOUR website!let x=number of balls whose number is >= 17
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we want
in a sample without replacement
P(X>=1) = 1-P(x=0) (Getting at least one is the same as the complement of getting none)
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P(x=0)=P(all 3 are numbered <17) = 
P(X>=1)=1-0.491=0.509
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This could also be solved as
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Permutations/333144: how do you order data sets according to increasing standard deviations when have same mean without computations 1 solutions
Answer 238697 by jrfrunner(365) on 2010-08-19 15:57:36 (Show Source):
You can put this solution on YOUR website!if you have the standard deviations and you want to order according to such criteria, is that simple.
first data set is the one with smalles std dev, then the next smallest std dev and so on.
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Probability-and-statistics/333068: A pizza shop owner determines the number of pizzas that are delivered each day. Find the mean, variance, and standard deviation for the distribution shown. If the manager stated that 45 pizzas were delivered on one day, do you think that this is a believable claim?
# of deliveries and probabilies
35 .1
36 .2
37 .3
38 .3
39 .1
I have all the answers (mean, variance, and standard deviation), I just need to know if 45 is believable and why? 1 solutions
Answer 238695 by jrfrunner(365) on 2010-08-19 15:47:03 (Show Source):
You can put this solution on YOUR website!just look at your data!
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your data shows that P(x<=39)=1.0
therefore, P(x=45) or "any" number greater than 39 is 0
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so, no such claim is not supported
If something happened that changed the process and it is not following history, in such case , collect new data to determine the support to such claims, but absence a change in process and based on existing data, the claim is not believable
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Angles/333124: my trig test says perform this calculation:
135 degrees 16'45" + 234 degrees 50"
How do I do that? 1 solutions
Answer 238690 by jrfrunner(365) on 2010-08-19 15:26:45 (Show Source):
You can put this solution on YOUR website!my trig test says perform this calculation:
135 degrees 16'45" + 234 degrees 50"
How do I do that?
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you basically have 135degrees 16' 45" + 234 degrees 0' + 50"
the 16' stands for 16 minutes
the 45" stands for 45 seconds
==
Note: 1degree=60' and 1'=60"
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you can add common things
so add 135degrees + 234 degrees = 369 degrees
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Now add the minutes
16' + 0'=16'
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Now add the seconds
45"+50"=95"
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so you basically have 369degrees 16' 95" (but wait!!!, this is not in reduced form)
95" can be reduced to 1'35"
--
so your answer is 369degrees 17' 35"
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Expressions-with-variables/332649: how do you solve for y in this equation : 3(5 + y) - y = 2y + 15 1 solutions
Answer 238682 by jrfrunner(365) on 2010-08-19 14:54:06 (Show Source):
You can put this solution on YOUR website!You cannot!
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to solve equations you need 1 equation for every unknown.
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You have one unknown (y), but you need 1 equation to solve it.
what you have provided is not a bonafide equation, its basically an expression duplicated in both sides, Which will just show that the left hand side equals the right hand side.
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Trigonometry-basics/333055: How do you solve this? And what type of math is it?
For 0 (degree symbol) is less than x is less than 90 (degree symbol), how many solutions are there for the equation 2 sin x = cos x 1 solutions
Answer 238680 by jrfrunner(365) on 2010-08-19 14:45:17 (Show Source):
You can put this solution on YOUR website!in mathematics, there are many ways to solve some problems.
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the domain  puts you in the first quadrant, where x=positive, y =positive
--
solve for x
 (divide both sides by sin(x)
 (invert both sides of the equation)

since x=26.565 resides within the domain  this is the answer
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Trigonometry-basics/333085: Verify the identity (sinx + cosx)^2=1 + sin2x 1 solutions
Answer 238672 by jrfrunner(365) on 2010-08-19 13:17:09 (Show Source):
You can put this solution on YOUR website!Verify the identity 
--
1. Expand the left hand side of the equation

2. simplify this result

--
now you need to utilize the property of Sin(a+b)=sin(a)*cos(b)+sin(b)*cos(a)
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Sin(2x)=sin(x+x)=sin(x)cos(x)+sin(x)*cos(x) = 2*sin(x)*cos(x)
--
therefore
 =  =
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Trigonometry-basics/333079: If cot t=1/3, and π < t < 3π/2, what is the value of sin t. 1 solutions
Answer 238671 by jrfrunner(365) on 2010-08-19 13:06:15 (Show Source):
You can put this solution on YOUR website!cot(t) =1/3 is the same as tan(t)=3
therefore
tan(t)=3 can be solved as t= Arctan(3)=71.565-/+n*180 (note 71.565 is in quadrant I and you want to be in quadrant III)
--
since the domain is restricted to π < t < 3π/2
This puts you in quadrant III where both x and y are negative.
--
so the answer is
t= Arctan(3)=71.565-/+180=251.565 (or -108.435)
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