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Please provide detailed answers OA are in Bold Face
Thanks!
1- Working alone, a small pump takes twice as long as a large pump takes to fill an empty tank. Working together at their respective constant rates, the pumps can fill the tank in 6 hours. How many hours would it take the small pump to fill the tank working alone?
(A) 8
(B) 9
(C) 12
(D) 15
(E) 18
2- On level farmland, two runners leave at the same time from the intersection of two country roads. One runner jogs due north at a constant rate of 8 miles per hour while the second runner jogs due east at a constant rate that is 4 miles per hour faster than the first runner’s rate. How far apart, to the nearest mile, will they be after 21hour?
(A) 6
(B) 7 (C) 8
(D) 12
(E) 14
3- If x = y + 4 and x = 20 – y, then (x^2) - (y^2)=
(A) 16
(B) 80
(C) 144
(D) 256 (E) 384
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Please provide detailed answers OA are in Bold Face
Thanks!
1- Working alone, a small pump takes twice as long as a large pump takes to fill an empty tank. Working together at their respective constant rates, the pumps can fill the tank in 6 hours. How many hours would it take the small pump to fill the tank working alone? (A) 8 (B) 9 (C) 12 (D) 15 (E) 18
2- On level farmland, two runners leave at the same time from the intersection of two country roads. One runner jogs due north at a constant rate of 8 miles per hour while the second runner jogs due east at a constant rate that is 4 miles per hour faster than the first runner’s rate. How far apart, to the nearest mile, will they be after 21hour? (A) 6 (B) 7 (C) 8 (D) 12 (E) 14
3- If x = y + 4 and x = 20 – y, then (x^2) - (y^2)= (A) 16 (B) 80 (C) 144 (D) 256 (E) 384
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The first one makes sense,
I'm not at all clear on the second. I make their rates 8 and 12 respectively. If they run at those rates North and East for 21 hours, I don't see how they can possibly be 7 miles apart.
I also dont get the answer to the third - I make it 80...
Please provide detailed answers OA are in Bold Face
Thanks!
1- Working alone, a small pump takes twice as long as a large pump takes to fill an empty tank. Working together at their respective constant rates, the pumps can fill the tank in 6 hours. How many hours would it take the small pump to fill the tank working alone? (A) 8 (B) 9 (C) 12 (D) 15 (E) 18
Show more
Solution:
If it takes twice as long to fill the tank, then the rate is half.
Solve for r, plugin in 6 hours as the time, 1 is 100% of the tank
(1/2)r(6) + r(6) = 1
r = 1/9
Remember this is the rate of the large pump, so 1/2*1/9 = 1/18 for the small pump's rate
solve for small pump t:
t = d/r
t = 1/(1/18) = 18
t = 1/(1/9)
Originally posted by yuefei on 14 Nov 2007, 18:30.
Last edited by yuefei on 14 Nov 2007, 18:33, edited 1 time in total.
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2- On level farmland, two runners leave at the same time from the intersection of two country roads. One runner jogs due north at a constant rate of 8 miles per hour while the second runner jogs due east at a constant rate that is 4 miles per hour faster than the first runner’s rate. How far apart, to the nearest mile, will they be after 21hour? (A) 6 (B) 7 (C) 8 (D) 12 (E) 14
Show more
Solution:
Setup a triangle with legs as the distance run by the runners. The hypotenuse is what we will solve for.
Runner A
8 miles / hour = 21 hours = 168 miles
Runner B
12 miles / hour = 252 miles
So triangle with a = 168 and b = 252
pythagoream theorem - However I at 21 hours I don't get 7.
Please provide detailed answers OA are in Bold Face
Thanks!
1- Working alone, a small pump takes twice as long as a large pump takes to fill an empty tank. Working together at their respective constant rates, the pumps can fill the tank in 6 hours. How many hours would it take the small pump to fill the tank working alone? (A) 8 (B) 9 (C) 12 (D) 15 (E) 18
2- On level farmland, two runners leave at the same time from the intersection of two country roads. One runner jogs due north at a constant rate of 8 miles per hour while the second runner jogs due east at a constant rate that is 4 miles per hour faster than the first runner’s rate. How far apart, to the nearest mile, will they be after 21hour? (A) 6 (B) 7 (C) 8 (D) 12 (E) 14
3- If x = y + 4 and x = 20 – y, then (x^2) - (y^2)= (A) 16 (B) 80 (C) 144 (D) 256 (E) 384
Show more
1: R is 1/x for small pipe so 2/x is rate for big pipe.
2- On level farmland, two runners leave at the same time from the intersection of two country roads. One runner jogs due north at a constant rate of 8 miles per hour while the second runner jogs due east at a constant rate that is 4 miles per hour faster than the first runner’s rate. How far apart, to the nearest mile, will they be after 21hour? (A) 6 (B) 7 (C) 8 (D) 12 (E) 14
Solution: Setup a triangle with legs as the distance run by the runners. The hypotenuse is what we will solve for.
Runner A 8 miles / hour = 21 hours = 168 miles Runner B 12 miles / hour = 252 miles
So triangle with a = 168 and b = 252 pythagoream theorem - However I at 21 hours I don't get 7.
Is there an an error in the question?
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Yes I am so sorry it is actually (1/2)hour. Copy Paste didn't work out so well!
Thank you for the detailed answer!!
I call shannagons on these problems except for 1. If you meant a half hour for question 2 I can see this b/c sqrt 52 ~ 7.
The third one is def. a typo. The answer is 80.
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For 2 - I get rates of 12 and 8 - so 4 and 6 respectively - so the distance between the runners will be sqrt of 4^2 + 6^2 = sqrt 36 + 16 = sqrt 52 - closest option is 7.
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