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Pumps A, B, and C operate at their respective constant

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Pumps A, B, and C operate at their respective constant [#permalink] New post 20 Feb 2007, 09:31
1.Pumps A, B, and C operate at their respective constant rates. Pumps A and B, operating simultaneously, can fill a certain tank in 6/5 hours; pumps A and C, operating simultaneously, can fill the tank in 3/2 hours; and pumps B and C, operating simultaneously, can fill the tank in 2 hours. How many hours does it take pumps A, B, and C, operating simultaneously to fill the tank?
A.1/3
B. ½
C.2/3
D.5/6
E.1

2.What is the tens digit of the positive integer r ?
(1) The tens digit of r/10 is 3.
(2) The hundreds digit of 10r is 6
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Re: Gmat Prep [#permalink] New post 20 Feb 2007, 10:53
jet1445 wrote:
1.Pumps A, B, and C operate at their respective constant rates. Pumps A and B, operating simultaneously, can fill a certain tank in 6/5 hours; pumps A and C, operating simultaneously, can fill the tank in 3/2 hours; and pumps B and C, operating simultaneously, can fill the tank in 2 hours. How many hours does it take pumps A, B, and C, operating simultaneously to fill the tank?
A.1/3
B. ½
C.2/3
D.5/6
E.1



If we consider the three groups of pumps, we see that the three groups can fill in one hour 5/6 +2/3+ 1/2=12/6=2 such tanks. Taken together, the three groups consist of 2 A's, 2 B's and 2 C's
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Re: Gmat Prep [#permalink] New post 20 Feb 2007, 13:04
Capacity of the tank is T.

A and B working together can fill tank in 6/5 hrs.
in one hr they can fill 5/6T

Similarly
in one hr B+C can fill 2/3T

in one hr C+A = 1/2T

Summing both sides

A+B+B+C+C+A working for 1 hour can fill 2T
2(A+B+C) working for an hour can fill 2T

A+B+C working for one hour can fill 1 T

2.What is the tens digit of the positive integer r ?
(1) The tens digit of r/10 is 3.
(2) The hundreds digit of 10r is 6[/quote]

B.
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Re: Gmat Prep [#permalink] New post 20 Feb 2007, 14:01
jet1445 wrote:
1.Pumps A, B, and C operate at their respective constant rates. Pumps A and B, operating simultaneously, can fill a certain tank in 6/5 hours; pumps A and C, operating simultaneously, can fill the tank in 3/2 hours; and pumps B and C, operating simultaneously, can fill the tank in 2 hours. How many hours does it take pumps A, B, and C, operating simultaneously to fill the tank?
A.1/3
B. ½
C.2/3
D.5/6
E.1

2.What is the tens digit of the positive integer r ?
(1) The tens digit of r/10 is 3.
(2) The hundreds digit of 10r is 6


For the second question:

Statement one tells you that when you % by 10 the tens digit is 3. You could have 380 or 320 and get 2 answers.

Statement 2 tells you when you * by 10 the hundreds digit is 6. From this statement you know the tens digit, because when you * by 10 the tens digit becomes the hundreds digit. For example, 267 * 10 = 2670
Re: Gmat Prep   [#permalink] 20 Feb 2007, 14:01
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