Question 41

Two pipes P and Q can fill a cistern in 18 and 24 minutes respectively. Both pipes are opened, but after some time, the slower pipe is closed. The cistern gets filled in 12 minutes from the start. When is the slower pipe closed?

Solution

P fill the cistern = 18 min

Q fill the cistern = 24 min

Total work done = LCM (18,24)= 72

P's efficiency = $$\frac{72}{18}$$ = 4

Q's efficiency = $$\frac{72}{24}$$ = 3

Tank will be fiiled= $$\frac{72}{7}$$hours

Tap P is open for 12 min and taps Q closed after some time

so

as we know that ,

efficiency multiplied by time = work

$$4\times 12 + 3\times T$$= 72

T = 8 min

Share on Whatsapp Share on Whatsapp

Create a FREE account and get: