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robertb answered: 4011 problems
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Probability-and-statistics/366535: What is the relationship between the Confidence Level and Type I Error?
1 solutions

Answer 261342 by robertb(4012) About Me  on 2010-11-05 21:21:34 (Show Source):
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Probability of Type I error = 1 - Confidence Level. For example, assigning a confidence level of 95% means you're only giving yourself 1 - 0.95 =0.05, or 5% chance of making a type I error, that is, a 5% window of making the mistake of rejecting the null hypothesis (status quo) when it is actually true.


Probability-and-statistics/366603: You wish to learn thge average of an MBA student within 2 years and with 99% confidence. How large of a sample data should you get. Describe the findings.
1 solutions

Answer 261341 by robertb(4012) About Me  on 2010-11-05 21:15:43 (Show Source):
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We can use Slovin's formula n+=+N%2F%281%2BNe%5E2%29, but what is the population N of MBA students?


Probability-and-statistics/366576: This is two questions I am having an issue with. The only two I cannot figure out. I really would appreciate it if there was a way you could scan the page back and upload it completed and how you did it? Thank you
Here is the uploaded page with 2 questions:
http://img525.imageshack.us/img525/2033/ccf1105201000000.jpg
1 solutions

Answer 261338 by robertb(4012) About Me  on 2010-11-05 21:10:37 (Show Source):
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Hmm. Get back to you soon. Got a class to teach.
Back now.
14.
a.) 525%2F1230+%2B-+2.325sqrt%28%28%28525%2F1230%29%2A%28705%2F1230%29%29%2F1230%29. This corresponds to the open interval (0.39404, 0.45962).
b.) No, it is not reasonable to conclude from the sample that the president is doing a good job. In fact we could say that the true proportion may be less than 50%. (As opposed to the null hypothesis that the true proportion is equal to or greater than 50%.)
15.
a.) $63/hr.
b.) Using the t-distribution with 22 degrees of freedom, the C.I. is 63%2B-+%282.508%29%2A%286.1%2Fsqrt%2823%29%29. This corresponds to the open interval (59.81, 66.19).
c.)We use the standard normal table again. We want 1%3E=1.645%2A%286.1%2Fsqrt%28n%29%29. This should give sqrt%28n%29%3E=10.0345, or n%3E=100.69. We can put n = 101.


Polynomials-and-rational-expressions/366567: 3x^2 − x − 4 factoring???
1 solutions

Answer 261335 by robertb(4012) About Me  on 2010-11-05 21:07:28 (Show Source):


Polynomials-and-rational-expressions/366566: 2x2 + 9x + 4 factoring???????/
1 solutions

Answer 261334 by robertb(4012) About Me  on 2010-11-05 21:06:32 (Show Source):
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(2x + 1)(x + 4)


Linear-equations/366680: solve using addition method
x - 2y = -1 and -x + 5y = 4
1 solutions

Answer 261333 by robertb(4012) About Me  on 2010-11-05 21:05:41 (Show Source):
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Adding corresponding sides, we get 3y = 3, or y = 1.
Substituting into the 1st equation, x - 2 = -1, or x = 1.


Points-lines-and-rays/366691: For each of the following, write the equation of the line determined by the given pair of points
a. (3,-7) and (3, -27)
b. (-4,5) and (-8,-7)

1 solutions

Answer 261328 by robertb(4012) About Me  on 2010-11-05 20:57:05 (Show Source):
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a. The line is a vertical line (same x-coordinates). The equation is x = 3.
b. %285--7%29%2F%28-4--8%29+=+%28y-5%29%2F%28x--4%29,
3+=+%28y-5%29%2F%28x%2B4%29,
3x%2B12+=+y-5,
y+=+3x%2B17.


Inequalities/366694: Please help me solve this problem, thanks in advance.
10y>9
1 solutions

Answer 261327 by robertb(4012) About Me  on 2010-11-05 20:52:09 (Show Source):
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y > 9/10, after dividing both sides by 10. (Direction of inequality doesn't change.)


Inequalities/366693: Please help me solve this problem, thanks in advance.
100>-5/3x +6>0
1 solutions

Answer 261326 by robertb(4012) About Me  on 2010-11-05 20:51:02 (Show Source):
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100-6 >-5/3x>-6,
94+%3E-5x%2F3%3E-6,
282%3E-5x%3E-18,
-282%2F5%3Cx%3C18%2F5.


Probability-and-statistics/366687: Why does the significance level differ among industries? Is the null hypothesis more likely to be rejected at α = 0.01 than α = 0.10? As the significance level increases to α = 0.10 from α = 0.01, which type error is more likely to occur? 7What may be done to reduce the likelihood of incurring this error?

1 solutions

Answer 261325 by robertb(4012) About Me  on 2010-11-05 20:47:16 (Show Source):
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Significance levels differ among industries because different industries hold different quality standards. The null hypothesis is more likely to be rejected at 0.10 significance level. As the significance level increases to α = 0.10 from α = 0.01, type I error is more likely to occur (that is, it is more likely that we reject a statement that may actually be true.) To reduce the likelihood of a type I error, continuous and periodic sampling within the industry is suggested (quality control) using as large (but manageble)a size as possible.


Linear-systems/366585: system of four linear algebraic equation (get values of A,B, C and D)
0= Acos(t)+Bsin(t)+Ctcos(t)+Dtsin(t)+3t-2
0=-Asin(t)+Bcos(t)+Ccos(t)-Ctsin(t)+Dsin(t)+Dtcos(t)+3
1=-Acos(t)-Bsin(t)-2Csin(t)-Ctcos(t)+2Dcos(t)-Dtsin(t)
1= Asin(t)-Bcos(t)-2Ccos(t)-Ccos(t)+Ctsin(t)-2Dsin(t)-Dsin(t)-Dtcos(t)
1 solutions

Answer 261324 by robertb(4012) About Me  on 2010-11-05 20:36:36 (Show Source):
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Let t = 0. Then the system becomes
0 = A-2,
0 = B+C+3,
1 = -A+2D,
1 = -B-2C-C, or 1 = -B - 3C.
The 1st equation gives A = 2.
Substitution into the 3rd equation gives 1 = -2 + 2D, or D = 3/2.
eliminating B from the 2nd and 4th equations gives C = 1.
Finally, substitution into the 2nd equation gives B=-4.


Exponential-and-logarithmic-functions/366682: My child is having trouble with Real exponents and exponential functions, and I don't understand how to do it in order to help her.
Problem: 13 square root6 * 13 square root 24 =
I don't know how to put square root on computor, sorry
1 solutions

Answer 261319 by robertb(4012) About Me  on 2010-11-05 20:19:21 (Show Source):


Linear_Equations_And_Systems_Word_Problems/366673: Graph (interval notation) |2x+1| greater than or equal to 5
1 solutions

Answer 261317 by robertb(4012) About Me  on 2010-11-05 20:12:22 (Show Source):
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|2x+1| >= 5 is the same as
2x+%2B1+%3C=-5 or 2x+%2B+1%3E=5.
2x%3C=-6 or 2x%3E=4.
x%3C=-3+or x%3E=2.
In interval notation, (-infinity, -3]U[2, infinity).


Probability-and-statistics/366676: There are 100 students. 40% of them have brown hair. 30% that have brown hair are boys. How many boys have brown hair?
1 solutions

Answer 261313 by robertb(4012) About Me  on 2010-11-05 20:06:35 (Show Source):
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Of the 100 students, 100*0.40 = 40 have brown hair. Of these, 40*0.30 = 12 are boys. So 12 boys have brown hair.


Trigonometry-basics/366643: Use sum of difference identities to find the exact value of sin(105°).
1 solutions

Answer 261301 by robertb(4012) About Me  on 2010-11-05 18:30:38 (Show Source):
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sin(105) = sin(60 + 45) = sin(60)*cos(45) + cos(60)*sin(45)
= %28sqrt%283%29%2F2%29%2A%28sqrt%282%29%2F2%29+%2B+%281%2F2%29%2A%28sqrt%282%29%2F2%29
=sqrt%286%29%2F4%29+ %28sqrt%282%29%29%2F4+
=%28sqrt%286%29%2B+sqrt%282%29%29%2F4+


Mixture_Word_Problems/366644: How many gallons of pure water must be added to 10 gallons of 30% saltwater to make a solution that is 25% saltwater?"
1 solutions

Answer 261294 by robertb(4012) About Me  on 2010-11-05 18:23:45 (Show Source):
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let x = # gallons pure water that must be added. Then
10*0.30 + x*0.00 = (10 + x)0.25,
3 = 2.5 + 0.25x,
0.5 = 0.25x
x = 2 gallons of water must be added.
***Note: x*0.00 denotes the weight contribution of the water to the salt content of the newly mixed solution. x is in gallons, and its salt concentration is 0.00 weight units per gallon, so that x*0.00 is in weight units.***


Probability-and-statistics/366646: How many scored between 600 and 750?
1 solutions

Answer 261293 by robertb(4012) About Me  on 2010-11-05 18:20:15 (Show Source):
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How many scored in what game? =D


Trigonometry-basics/366656: Solve sin^2(x)csc(x)-1=0 for 0°≤x<360°.
1 solutions

Answer 261292 by robertb(4012) About Me  on 2010-11-05 18:18:33 (Show Source):
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The left-hand side is reducible to sinx. Hence we solve sinx = 1. Only one angle satisfies that, x = 90 degrees.


Inequalities/366654: 11. Name the axis or quadrant in which the point lies. (6, -2/3)
1 solutions

Answer 261291 by robertb(4012) About Me  on 2010-11-05 18:15:50 (Show Source):


Inequalities/366653: 8. The ordered pair (-2, 3) is a solution of y = -2x + 7.
1 solutions

Answer 261290 by robertb(4012) About Me  on 2010-11-05 18:15:03 (Show Source):
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False. Just substitute the coordinates of the given point into the equation.


Evaluation_Word_Problems/366442: Find an equation of variation for the given situation.
y varies inversely as the square of x, and y = 7 when x = 3
1 solutions

Answer 261151 by robertb(4012) About Me  on 2010-11-05 07:23:55 (Show Source):
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y+=+k%2Fx%5E2 from the inverse relationship, where k is the constant of proportionality. When y = 7, x = 3, so 7+=+k%2F3%5E2+=+k%2F9. Hence k = 63, and therefore the variation equation is y+=+63%2Fx%5E2.


Trigonometry-basics/366464: Find all values of theta in the interval 0°< theta <360° that satisfy the equation 2(sin theta +csc theta)=5
1 solutions

Answer 261150 by robertb(4012) About Me  on 2010-11-05 07:13:59 (Show Source):
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sin+%28theta%29+%2B+csc+%28theta%29+=+5%2F2,
sin+%28theta%29+%2B1%2Fsin+%28theta%29+=+5%2F2,
%28%28sin+%28theta%29%29%5E2+%2B1%29%2Fsin%28theta%29+=+5%2F2,
2%28sin+%28theta%29%29%5E2+%2B2=+5sin%28theta%29+,
2%28sin+%28theta%29%29%5E2+-+5sin%28theta%29%2B2=+0,
%282sin%28theta%29-1%29%28sin%28theta%29-2%29+=+0. The first factor gives
2sin%28theta%29+=+1, or sin%28theta%29=1%2F2, giving theta = 30 or 150 degrees.
The second factor sin%28theta%29-2+=+0 does not give any solutions. (Why?)


Functions/366461: How do I solve the following to THREE decimal places?
ln x + ln(x+7) = -5
1 solutions

Answer 261149 by robertb(4012) About Me  on 2010-11-05 07:01:16 (Show Source):
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ln+x+%2B+ln%28x%2B7%29+=+-5
ln%28x%28x%2B7%29%29+=+ln%28x%5E2%2B7x%29+=+-5,
Hence+x%5E2%2B7x+=+e%5E-5, or+x%5E2%2B7x+-+e%5E-5+=+0 . Using the quadratic formula:
. The values are, to 3 decimal places, 0.001 (from 0.000962432), or -7.0001 (from -7.000962432). We have to eliminate the 2nd value, because it won't satisfy the original equation. The answer is 0.001.


Functions/366460: how do i find the domain of f(x)=2-ln(7x)?
and the domain of f(x)=log(4)(x-4)^2?
I am struggling with these....typical for someone out of math for 25 years.
1 solutions

Answer 261146 by robertb(4012) About Me  on 2010-11-05 06:49:17 (Show Source):
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For the first function must make sure that 7x >0, or x>0 (after dividing both sides of the inequality by 7).
For the second function, %28x-4%29%5E2+%3E0. This is just the set of all real numbers except x = 4.


Miscellaneous_Word_Problems/366291: A 6x6x6 cube is constructed of 1x1x1 cubes. The faces of the large cube are then painted. How many of the smaller cubes have no painted side?
1 solutions

Answer 261144 by robertb(4012) About Me  on 2010-11-05 06:44:34 (Show Source):
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All of the 4%5E3+=+64 1x1x1 cubes hidden inside the 6x6x6 cube.


Trigonometry-basics/366440: Verify the identity: (cos x-sin x)^2=1-sin2x
1 solutions

Answer 261143 by robertb(4012) About Me  on 2010-11-05 06:39:43 (Show Source):


Probability-and-statistics/366318: The length of a Colorado brook trout is normally distributed. What is the probability that a brook trout’s length:a.) exceeds the mean?b.) exceeds the mean by at least 1 standard deviation?c.) exceeds the mean by at least 2 standard deviations?d.) is within 2 standard deviations?
1 solutions

Answer 261142 by robertb(4012) About Me  on 2010-11-05 06:35:20 (Show Source):
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By the property of a normal distribution, the probability that a brook trout's length a.)exceeds the mean is 0.50,
b.) exceeds the mean by at least 1 standard deviation is about 0.16 (by adjusting the 68-95-99.7 rule),
c.)exceeds the mean by at least 2 standard deviations is about 0.025(by adjusting the 68-95-99.7 rule),
d.)is within 2 sd's is 0.95.


Functions/366308: I am in the process of learning these things and a way to make it more interesting besides the ol' make it into a word problem thing. Can you help me
1 solutions

Answer 261138 by robertb(4012) About Me  on 2010-11-05 06:21:27 (Show Source):
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Choose a particular topic and ask a question... =)


Probability-and-statistics/366449: In a game, there are three rounds; the probabilities of winning first, second & third rounds are 3/4 , 1/2 and 1/4 respectively. A prize will be given, if any one wins all the rounds. What is the probability of winning the prize?
A. 29/32 B. 1/32 C. 9/32 D. 3/32 E. none
1 solutions

Answer 261136 by robertb(4012) About Me  on 2010-11-05 06:20:19 (Show Source):
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Assuming the 3 events are mutually independent (i.e., performance in the next round is not affected by the previous round), the probability is %283%2F4%29%281%2F2%29%281%2F4%29+=+3%2F32. The answer is D.


Probability-and-statistics/366456: SUPPOSE that X Is a discrete random variable with p(X+0)=.25,P(X+2)=.125 AND P(X=3)=.5.PLOT THE PROBABILITY MASS FUNCTION AND CUMULATIVE DISTRUTION FUNCTION OF X.

1 solutions

Answer 261134 by robertb(4012) About Me  on 2010-11-05 06:14:34 (Show Source):
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I got a feeling you meant the following:
p(X=0)=.25,
P(X=1)=.125
P(X=2)=.125 and
P(X=3)=.5, right?
The cumulative distribution function is
F(X = 0) = 0.25
F(X = 1) = 0.375
F(X = 2) = 0.5
F(X = 3) = 1.
It's easy to plot the probability mass function for this distribution.


Permutations/366458: Using permutations, how do we solve this problem: How many distinguishable 6 letter "words" can be formed using the letters in LONDON? the answer is 180, but I can't figure out how to solve it. Please help.
1 solutions

Answer 261132 by robertb(4012) About Me  on 2010-11-05 06:08:06 (Show Source):
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There are 2 o's, 2 n's, 1 l, and 1 d in the word "london". Then from a formula from combinatorics , there are 6%21%2F%282%212%211%211%21%29+=+720%2F4+=+180ways.