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richard1234 answered: 5385 problems
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Evaluation_Word_Problems/403131: what do you use as reasons to support the steps of a geometric proof?
1 solutions

Answer 285087 by richard1234(5390) About Me  on 2011-02-01 21:27:13 (Show Source):
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Whatever theorems or steps are necessary.


Quadratic_Equations/403093: what is the slope of 2x+4
1 solutions

Answer 285084 by richard1234(5390) About Me  on 2011-02-01 21:24:49 (Show Source):
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If f(x) = 2x+4 then the slope is 2 (since it's already in mx + b form).


Polynomials-and-rational-expressions/402998: I NEED HELP WITH POLYNOMIALS. MY PROBLEM IS -4y^3-20y^2-24, problem two is x^2+3xy-28y^2
1 solutions

Answer 285079 by richard1234(5390) About Me  on 2011-02-01 21:13:22 (Show Source):
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What is your question?


Unit_Conversion_Word_Problems/403048: If a test has 100 questions and you get 92 of them right, what decimal number would that represent?
1 solutions

Answer 285078 by richard1234(5390) About Me  on 2011-02-01 21:12:03 (Show Source):


Probability-and-statistics/403119: Winning a race: The odds against Paul Phillips winning the 100 yard dash are 7:2. Determine the probability that a) Paul wins and b)Paul doesn't win. What would the formula be for solving this problem. I know that there are 9 chances that he will win because the sum of 2 and 7. Where do I go from there? I need the formula so I can show my work. Thank you for your help!
1 solutions

Answer 285077 by richard1234(5390) About Me  on 2011-02-01 21:10:48 (Show Source):
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Paul has 7 of those 9 "chances" so the probability he wins is 7/9. Therefore the probability he doesn't win is 1 - 7/9, or 2/9.


Numbers_Word_Problems/403059: I am a number between 10 and 20. My tens digit is 1. Each digit to the right is twice as great as the digit before it. What is the value of the digit in the hundredths place?
1 solutions

Answer 285074 by richard1234(5390) About Me  on 2011-02-01 21:07:41 (Show Source):
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12.48 is the number (just increasing powers of 2), and the hundredths digit is 8.


Evaluation_Word_Problems/402713: a quadrilateral has angles 70degres , 90degres , 2x and 3x ,what is the value of x?and show me the formula.
1 solutions

Answer 284848 by richard1234(5390) About Me  on 2011-02-01 09:20:07 (Show Source):
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The sum of the interior angles in a quadrilateral is 360 degrees. Thus,

70 + 90 + 2x + 3x = 360

160 + 5x = 360

x = 40


Volume/402702: rain which falls onto a flat rectangular surface of length 6 m and width 4 m is collected in a cylinder of internal radius 20 cm. What is the depth of water in the cylinder after a storm in which 1 cm of rain fell?

1 solutions

Answer 284816 by richard1234(5390) About Me  on 2011-02-01 07:53:28 (Show Source):
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I would say 1 cm because 1 cm of rain fell...


Linear-systems/402594: did you hear about the mathematician who wanted to make a fruit salad, so he brought some apples and oranges _ _ _ _ _ _ _ _ _?
1 solutions

Answer 284766 by richard1234(5390) About Me  on 2011-01-31 22:32:59 (Show Source):
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...and put them in his Klein bottle.


Miscellaneous_Word_Problems/402186: Suppose f(x)equals the greatest integer less than or equal to x. So, for example, f(1.99)=1, f(2)=2, and f(4.87)=4. Find the limit as x tends to 2 from the left.
lim
x→2- f(x)

1 solutions

Answer 284764 by richard1234(5390) About Me  on 2011-01-31 22:28:42 (Show Source):
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lim%28x-%3E2%2C+f%28x%29%29+=+1 (should be x->(2-) but the site won't parse 2-) since all f(x) values where x is less than 2 are equal to 1.


Equations/402316: write an equation using f for the number of faces, e for the number of edges and v for the number of vertices.
What is the relationship of the number of edges and the number of vertices in a cube?
1 solutions

Answer 284762 by richard1234(5390) About Me  on 2011-01-31 22:20:12 (Show Source):
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There is a formula named after Euler that says that F + V - E = 2, for any polyhedron. A cube has six faces, eight vertices, and twelve edges, and satisfies, since 6 + 8 - 12 = 2. An interesting fact is that Euler's formula can be applied to higher dimensions, including 4-, 5-, ... dimensional manifolds.


Numbers_Word_Problems/402344: The counting numbers are 1,2,3,4, and so on. If the sum of three different, odd counting numbers is less than 10, what is the largest of the three?
CLUE: The answer is less than 9.

1 solutions

Answer 284760 by richard1234(5390) About Me  on 2011-01-31 22:15:32 (Show Source):
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The counting numbers 1, 3, 5 add up to 9, which is less than 10. However, if we choose any other set of three distinct counting numbers, the sum would be at least 10 (since we know that {1, 3, 5} has the minimal sum). Therefore {1, 3, 5} is the only such set and the largest of the numbers is 5.


Triangles/402302: If AC = 20 centimeters, and BC = 16 centimeters, which does AB equal?

1 solutions

Answer 284758 by richard1234(5390) About Me  on 2011-01-31 22:12:48 (Show Source):
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Not enough information...AB can be anything between 4 and 36 centimeters.


Probability-and-statistics/402353: In how many different ways can a 10-question true-false test be answered if it is all right to leave questions unanswered?
1 solutions

Answer 284756 by richard1234(5390) About Me  on 2011-01-31 22:02:27 (Show Source):
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For each question, you can either answer it true, answer false, or leave it blank. This is 3 ways for each of 10 questions, so the total number of ways is 3%5E10.


Travel_Word_Problems/402443: A golf ball is launched upward with an initial speed of 30 m/sec by a golfer atop the Washington Monument, which is 160 m above the ground. How high above the ground will the ball be after 3 sec?
I'm not sure how to set this up. Should I use: distance = rate × time?

1 solutions

Answer 284753 by richard1234(5390) About Me  on 2011-01-31 21:56:23 (Show Source):
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Distance = rate*time only works for constant velocity problems. In this problem, we have the acceleration due to gravity.

The formula for determining position given a constant acceleration is X+=+%281%2F2%29at%5E2+%2B+v%5B0%5Dt+%2B+x%5B0%5D, where a = -9.81 m/s^2, v%5B0%5D is the original velocity, x%5B0%5D is the original position (this equation is derived using integral calculus). Here, t = 3 s, v%5B0%5D = 30 m/s, x%5B0%5D = 160 m. Therefore,

X+=+%281%2F2%29%28-9.81m%2Fs%5E2%29%283s%29%5E2+%2B+%2830m%2Fs%29%283s%29+%2B+160m = 205.9 meters


Surface-area/402598: What is the formula for the perimeter of a rectangle?
1 solutions

Answer 284744 by richard1234(5390) About Me  on 2011-01-31 21:46:56 (Show Source):
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2(L+W) where L is the length and W is the width


Coordinate-system/402491: write a formula that expresses the relationship described by each statement. Use k for the constant in each case. T varies directly as h.
1 solutions

Answer 284740 by richard1234(5390) About Me  on 2011-01-31 21:39:26 (Show Source):


Trigonometry-basics/402561: verify the identity:
(cos^2x)-(sin^2x)=(1-2sin^2X)
1 solutions

Answer 284739 by richard1234(5390) About Me  on 2011-01-31 21:37:10 (Show Source):
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Using the identity cos%5E2%28x%29+%2B+sin%5E2%28x%29+=+1, if we subtract 2sin%5E2%28x%29 from both sides, we obtain cos%5E2%28x%29+-+sin%5E2%28x%29+=+1+-+2sin%5E2%28x%29 and we're done.


Miscellaneous_Word_Problems/402565: 1. In this problem, we analyze the profit found for sales of graphic t-shirts. A demand equation (sometimes called a demand curve) shows how much money people would pay for a product depending on how much of that product is available on the open market. Often, the demand equation is found empirically (through experiment, or market research).
a. Suppose a market research company finds that at a price of p = $25, they would sell x = 60 shirts each month. If they lower the price to p = $15, then more people would purchase the shirts, and they can expect to sell x = 75 shirts in a month’s time. Find the equation of the line for the demand equation. Write your answer in the form p = mx + b. Hint: Write an equation using two points in the form (x, p). Show all your work.
A company’s revenue is the amount of money that comes in from sales, before business costs are subtracted. For a single product, you can find the revenue by multiplying the quantity of the product sold, x, by the demand equation, p.
b. Substitute the result you found from part a. into the equation R = xp to find the revenue equation. Provide your answer in simplified form. Show all your work.

The costs of doing business for a company can be found by adding fixed costs, such as rent, insurance, and wages, and variable costs, which are the costs to purchase the product you are selling. The portion of the company’s fixed costs allotted to this product is $600, and the supplier’s cost for a shirt is $18 each. Let x represent the number of shirts.

c. If b represents a fixed cost, what value would represent b? Show all your work.
d. Find the cost equation for the shirt. Write your answer in the form C = mx + b. Show all your work.
The profit made from the sale of shirts is found by subtracting the costs from the revenue.
e. Find the Profit Equation by substituting your equations for R and C in the equation . Simplify the equation. Show all your work.

f. What is the profit made from selling 33 shirts per month? Show all your work.
g. What is the profit made from selling 27 shirts each month? Show all your work.

h. What is the profit made from selling no shirts each month? Interpret your answer. Show all your work.

i. Use trial and error to find the quantity of shirts per month that yields the highest profit. Show all your work.
j. How much profit would you earn from the number you found in part i? Show all your work.
k. What price would you sell the shirts at to realize this profit? Hint: Use the demand equation from part a. Show all your work.

1 solutions

Answer 284736 by richard1234(5390) About Me  on 2011-01-31 21:35:44 (Show Source):
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I don't think I or any tutor will answer all 11+ parts to this question...but I'll get you started and you can finish the rest.

To find the linear equation, we have two ordered pairs (25, 60) and (15, 75) (here, the price is the x-variable, however normal demand curves list the number sold as the x-variable). The slope m is equal to m+=+DELTA%28y%29%2FDELTA%28x%29+=+15%2F-10+=+-3%2F2%29 so m = -3/2. To find the y-intercept replace m, as well as an ordered pair to obtain

60 = (-3/2)(25) + b --> 60 = -75/2 + b --> b = 195/2 = 97.5

The demand equation is therefore given by p+=+%28-3%2F2%29x+%2B+97.5. You should be able to figure out the rest of the problems. Btw, part i) does not require trial and error, since the revenue is given by px, we have a quadratic equation that we can optimize using the vertex of the quadratic, or by the derivative.


Miscellaneous_Word_Problems/401837: Please Explain the difference between 2n+2 and 2(n+2). EXPLAIN PLEASE
1 solutions

Answer 284445 by richard1234(5390) About Me  on 2011-01-30 22:13:55 (Show Source):
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The 2 in the product 2(n+2) distributes over n and 2, giving 2(n) + 2(2) = 2n + 4.


Linear-equations/401989: tell whether each equation represents direct or inverse variation:
y=80x
xy=80
y=80/x
y/x=80
1 solutions

Answer 284443 by richard1234(5390) About Me  on 2011-01-30 22:07:20 (Show Source):
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The first and fourth equations are equivalent, and they represent direct variation because when x increases, y also increases by the same ratio. The second and third equations are equivalent and they represent inverse variation because when x increases, y decreases (and vice versa).


Word_Problems_With_Coins/396775: Using only quarters, nickels, dimes and pennies--how many ways can I make 0.99? (99 cents)
1 solutions

Answer 284440 by richard1234(5390) About Me  on 2011-01-30 21:50:40 (Show Source):
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Note that this is equivalent to finding the number of ways to make 95, 90, 85, ..., 0 cents using quarters, nickels, and dimes since the pennies will be uniquely determined afterwards. Also, we can further reduce this to make 19, 18, 17, ..., 0 cents using 5 cent, 2 cent, and 1 cent pieces (for example, 3 quarters, 1 dime, 2 nickels making 95 cents is equivalent to 3 5-cent pieces, 1 2-cent piece, 2 1-cent pieces making 19 cents). In essence, we have established a bijective function that maps some set of numbers to a set that is a bit easier to count.

Therefore we want to find the number of ways to make 0 cents, 1 cent, ..., 19 cents (using 5-cent, 2-cent, 1-cent pieces), and add them up. Here, I will demonstrate the number of ways to make x cents *without* using a 5-cent piece:

Case 0: We wish to make 0 cents --> 1 way (just use no coins)
Case 1: We wish to make 1 cent --> 1 way 2*0 + 1*1
Case 2: We wish to make 2 cents --> 2 ways 2*1 + 1*0; 2*0 + 1*2
Case 3: We wish to make 3 cents --> 2 ways 2*1 + 1*1; 2*0 + 1*3
Case 4: We wish to make 4 cents --> 3 ways 2*2 + 1*0; 2*1 + 1*2, 2*0 + 1*4
Case 5: We wish to make 5 cents --> 3 ways 2*2 + 1*1, 2*1 + 1*3, 2*0 + 1*5

There is a pattern, which we can prove by a simple induction or modular arithmetic argument, that the number of ways to make k cents increments by 1 every 2 cents. We can generalize and say that the number of ways to make k cents without using a 5-cent piece is floor%28k%2F2%29+%2B+1 where floor%28z%29 represents the floor value of z. Summing up from k = 0 to k = 19,

sum%28%28floor%28k%2F2%29%2B1%29%2C+k+=+0%2C+19%29+=+1+%2B+1+%2B+2+%2B+2+%2B+3+%2B+3+... +9+%2B+9+%2B+10+%2B+10 = 110.

Now, suppose 5+%3C=+k+%3C=+19 and we wish to count the number of ways to make k cents using exactly one 5-cent piece. We can note that this is analogous to computing the ways of making 0 to 14 (subtracting 5 from all terms). In other words, we have

sum%28%28floor%28k%2F2%29%2B1%29%2C+k+=+0%2C+14%29+=+1+%2B+1+%2B+2+%2B+2 + ... + 7+%2B+7+%2B+8 = 64

Repeat the same with the cases where two 5-cent pieces and three 5-cent pieces are used. Basically, only the bounds are changed to {0, 9}, {0, 4}.

sum%28%28floor%28k%2F2%29%2B1%29%2C+k+=+0%2C+9%29+=+1+%2B+1+%2B+2+%2B+2 + ... + 4+%2B+4+%2B+5+%2B+5 = 30

sum%28%28floor%28k%2F2%29%2B1%29%2C+k+=+0%2C+4%29+=+1+%2B+1+%2B+2+%2B+2+%2B+3 = 9

Adding all these values up, we get 110 + 64 + 30 + 9 = 213 ways. Since our function is bijective, we can say that the number of ways to make 99 cents is also equal to 213.


This solution required the use of a bijective function, which is normally not taught in a standard middle/high school curriculum. Here is a Wikipedia article in case you're interested: http://en.wikipedia.org/wiki/Bijection







Rectangles/401990: THE PERIMETER OF A RECTANGLE IS 34 CM. HOW DO YOU SOLVE FOR THE LENGTH AND HEIGHT?
1 solutions

Answer 284413 by richard1234(5390) About Me  on 2011-01-30 20:54:07 (Show Source):
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We have 2(L+H) = 34 --> L+H = 17. So L = 17-H, H = 17-L.


Linear-systems/401954: the width of a rectangle is 4 feet less then the lenght. the area is 5ft sqaured whats the legth and width ?
1 solutions

Answer 284411 by richard1234(5390) About Me  on 2011-01-30 20:51:07 (Show Source):
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Width = 1 ft, Length = 5 ft. It's possible to do this without the quadratic formula since the only factors of 5 are 5 and 1, which differ by 4. However the surefire way is to use the quadratic formula.


Equations/401961: i have been working on this problem for quite a while and cant seem to get it right without using a calculator. my question is -3+3y=2y+5. thank you so much. it is very appreciated.
1 solutions

Answer 284409 by richard1234(5390) About Me  on 2011-01-30 20:45:28 (Show Source):
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No calculator required...we have

-3 + 3y = 2y + 5 Adding -2y to both sdies,

-3 + y = 5

y = 8


Rational-functions/401959: what is Y=-3x+3 graphed?
1 solutions

Answer 284407 by richard1234(5390) About Me  on 2011-01-30 20:43:04 (Show Source):


Linear-equations/401645: Please I really need help with this equation
2u-9=7u+15-u-20
Could you show me step by step how to solve it
1 solutions

Answer 284262 by richard1234(5390) About Me  on 2011-01-30 08:50:46 (Show Source):
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Combine like terms on both sides to get

2u - 9 = (7u - u) + (15 - 20) = 6u - 5

Add -2u to both sides to get

-9 = 4u - 5

Add 5 to both sides to get
-4 = 4u --> u = -1.


Triangles/401653: The length of the hypotenuse of a right-angled triangle is 17 cm. The base of the triangle is 7 cm
more than the height. Find the height of the triangle.
I looked at the answer from the answers book it said height = 8cm, then I worked out this is because of pythagoras' theorem.
However I don't know how with the information given you would put this in a quadratic equation and work it out, for the question I need to show working out which I am confused of because I don't know the steps of working out, please help.
1 solutions

Answer 284261 by richard1234(5390) About Me  on 2011-01-30 08:41:21 (Show Source):
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If you recall the 8-15-17 Pythagorean triple, you can conclude the base is 15 and the height is 8.

Or, we can turn this into a quadratic by letting the height be h and the base h+7. Then,

h%5E2+%2B+%28h%2B7%29%5E2+=+17%5E2+=+289

2h%5E2+%2B+14h+%2B+49+=+289

2h%5E2+%2B+14h+-+240+=+0

h%5E2+%2B+7h+-+120+=+0 (dividing by 2)

%28h-8%29%28h%2B15%29+=+0

h = 8 (taking the positive solution).


Mixture_Word_Problems/401640: how many gallons of milk that is 2% butterfat must be mixed with milk that is 3.5% butterfat to get 10 gallons that is 2% butterfat
1 solutions

Answer 284260 by richard1234(5390) About Me  on 2011-01-30 08:37:44 (Show Source):
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10 gallons of 2% butterfat. If we mixed some 3.5% butterfat milk, then the average amount of butterfat would exceed 2%.


Number-Line/401519: how do i work this problem out step by step
find the equivalent expression with the given denominator
7/n =?/n2
1 solutions

Answer 284212 by richard1234(5390) About Me  on 2011-01-29 23:24:22 (Show Source):
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7%2Fn+=+x%2Fn%5E2

Cross multiplying, 7n%5E2+=+xn --> x = 7n.


Equations/401445: Determine whether the ordered pair is a solution of the given equation:
(-2,3); x + 2y = -2

The answer book says Yes....I keep coming up with No.
Please help.
1 solutions

Answer 284209 by richard1234(5390) About Me  on 2011-01-29 23:10:23 (Show Source):
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In fact you're right...an ordered pair lies on the function if (and only if) equality occurs. Here, if we replace x = -2 and y = 3,

-2 + 2(3) = -2

-2 + 6 = -2, not true, so the ordered pair doesn't lie on the line.