Question

Three pipes A, B, and C can fill the tank in 10 hours, 20 hours and 40 hours respectively. In the beginning, all of them are opened simultaneously. After 2 hours, tap C is closed and A and B are kept running. After the 4th hour, tap B is also closed. The remaining work is done by tap A alone. What is the percentage of the work done by tap A alone?

• A. 30%
• B. 35%
• C. 45%
• D. 50%
• E. None of these

Answer 1

The correct option is B 35%

Pipe A's work in % =100/10=10%
Pipe B's work in %=100/20=5%
Pipe C's work in %=10040=2.5%
All of them are opened for 2 hours
After 2 hours, tap C is closed
After the 4th hour, tap B is also closed =100
$\Rightarrow (10+5+2.5)\times 2+(10+5)\times 2$+ work done by tap A alone=100
$\Rightarrow$ 35+30+work by tap A alone=100
$\Rightarrow$ work by tap A alone =100-65=35%