Pipe A can fill a tank in 90 minutes. Pipe B whose diameter is 3 times

Question

Pipe A can fill a tank in 90 minutes. Pipe B whose diameter is 3 times that of Pipe A also fills the tank. lf both the pipes are kept open when the tank is empty, how long will the pipes take to fill the tank

A) 7 minutes
B) 9 minutes
C) 5 minutes
D) 6 minutes

A) 7 minutes
B) 9 minutes
C) 5 minutes
D) 6 minutes
E) 10 minutes

GMATinsight · Accepted Answer

Pipe A = 90 Minutes
Pipe B = 3 times diameter of A = 3^2 times volume of A = (1/9) time of A = (1/9)*90 = 10 minutes

Volume  = πr^2h

Let, Tank capacity = 90 Liters

Volume input by tank A in 1 minute = 90/90 = 1 liter
Volume input by tank B in 1 minute = 90/10 = 9 liter

Volume input by tank A and B both in 1 minute = 1+9 = 10 liter

Time for both = 90/10 = 9 minutes

Answer: Option B

ankban · Answer

The rate of pipe B will be directly proportional to square of radius of pipe A. Assume the pipes to be cylinders with equal lengths ( height in the formula ), then 
volume of that cylinder = π r^2 h
so the time taken will be inversely proportional to square of radius. 
time taken by pipe B = 90/ 3^2 = 10min
Now we can easily find time taken when both are open simultaneously.

Posted from my mobile device

CAMANISHPARMAR · Answer

Though the question is not that difficult, what is the source of this question? It does not seem like a GMAT question. Also, the number of options is 4 (not the standard 5)

anuspn · Answer

CAMANISHPARMAR

Thanks for highlighting the number of options.

Source of the question is wizako  WizakoBaskar

Regards,
Anurag Jha

saynchalk · Answer

Question: These types of questions will not come for the Focus Edition, right? Yet to see these types of questions on the practice tests

Dbrunik · Answer

bb  can we get this question taken out of the quiz pool for Focus edition ?

Bunuel · Answer

Added the Geometry tag. That should remove the question from the quiz. Thank you.

Pipe A can fill a tank in 90 minutes. Pipe B whose diameter is 3 times

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Pipe A can fill a tank in 90 minutes. Pipe B whose diameter is 3 times

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