Quantitative Aptitude – Arithmetic – Pipes and Cisterns – A tank is emptied every day

Slot -2 – Quantitative Aptitude – Arithmetic – Pipes and Cisterns – A tank is emptied every day at a fixed time

A tank is emptied every day at a fixed time point. Immediately thereafter, either pump A or pump B or both start working until the tank is full. On Monday, A alone completed filling the tank at 8 pm. On Tuesday, B alone completed filling the tank at 6 pm. On Wednesday, A alone worked till 5 pm, and then B worked alone from 5 pm to 7 pm, to fill the tank. At what time was the tank filled on Thursday if both pumps were used simultaneously all along?

a) 4:24 pm
b) 4:12 pm
c) 4:48 pm
d) 4:36 pm

Answer: a) 4 : 24 pm

Solution:
Let pump A alone can fill the tank in t hours so time taken by pump B alone = t-2 hours
As per question , (t-3)/t+2/(t-2)=1
t^2-3t+6=t^2-2t
Or t=6
So the time at which pumps tank is emptied = 8 pm – 6 hours = 2 pm
Time taken by both pumps together to fill the tank =(6×4)/(6+4)=2.4 hours=2 hour 24 minutes
Thus tank will be filled by 2 pm + 2 hour 24 minutes=4:24 pm

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