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Ev123
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A Few Official GMAT Test 48 Questions! 14 Nov 2007, 18:11
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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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alrussell
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A Few Official GMAT Test 48 Questions! 14 Nov 2007, 18:22
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Ev123
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


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...
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yuefei
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A Few Official GMAT Test 48 Questions! 14 Nov 2007, 18:23
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Ev123
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)
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A Few Official GMAT Test 48 Questions! Updated on: 14 Nov 2007, 18:33
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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Ev123

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.

Is there an an error in the question?
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GMATBLACKBELT
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A Few Official GMAT Test 48 Questions! 14 Nov 2007, 18:30
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Ev123
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.

1/x+2/x=1/6 --> x=18
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Ev123
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A Few Official GMAT Test 48 Questions! 14 Nov 2007, 18:35
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yuefei
Ev123

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?
Show more



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!!
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yuefei
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A Few Official GMAT Test 48 Questions! 14 Nov 2007, 18:36
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Blackbelt method for Q2 is much easier. Where s and t are amount completed in 1 hour.

1/s + 1/t = 1/t
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A Few Official GMAT Test 48 Questions! 14 Nov 2007, 18:41
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168^2 + 252^2 = c^2 = 7

This does not equal 7.



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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alrussell
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A Few Official GMAT Test 48 Questions! 14 Nov 2007, 18:44
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GMATBLACKBELT
168^2 + 252^2 = c^2 = 7

This does not equal 7.



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.
Show more

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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yuefei
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A Few Official GMAT Test 48 Questions! 14 Nov 2007, 18:45
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I agree. Isn't there something in the forum rules about shenanigan's :)
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Ev123
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A Few Official GMAT Test 48 Questions! 15 Nov 2007, 07:39
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I agree on Question 3!

I kept getting 80. Really confused about the official answer.

I should call GMAT and ask for an automatic 800 for finding a mistake on their study materials ;)

Do you think it will work?! lol.

Thanks for the help guys I really appreciate it!

~ Ev



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Hi there,
This topic has been closed and archived due to inactivity or violation of community quality standards. No more replies are possible here.
Where to now? Join ongoing discussions on thousands of quality questions in our Quantitative Questions Forum
Still interested in this question? Check out the "Best Topics" block above for a better discussion on this exact question, as well as several more related questions.
Thank you for understanding, and happy exploring!