Question

two taps a and b can fill a cistern in 30 minutes and 45 minutes respectively. There is third exhaust tap C at the bottom .If all the taps are opened at the same time the cistern will be full in 45 min. In what time can exhaust tap C empty the cisterh when full?

Answer 1

Given taps X and Y can fill the tank in 30 and 40 minutes respectively. Therefore,

 

part filled by tap X in 1 minute = 1/30

 

part filled by tap Y in 1 minute = 1/40

 

Tap Z can empty the tank in 60 minutes. Therefore,

 

part emptied by tap Z in 1 minute = 1/60

 

Net part filled by Pipes X,Y,Z together in 1 minute = [1/30 +1/40 - 1/60] = 5/120 = 1/24

 

i.e., the tank can be filled in 24 minutes.

Here just replace 40 min to 45 minute.

Answer 2

45 min will be the answer