| A tank can be filled by a tap in 20 min and by another tap in 60 min. Both the taps are kept open for 5 min and then the 1st tap is shut off. After this, how much time the tank will be completely filled? |
A) 20 min
B) 30 min
C) 45 min
D) 40 min
Correct Answer: C
Solution :
| Part of the tank filled by both taps in 5 min |
| \[=5\times \left( \frac{1}{20}+\frac{1}{60} \right)=\frac{5\times (6+2)}{120}=\frac{8}{24}=\frac{1}{3}\] |
| \[\therefore \]Remaining part \[=\left( 1-\frac{1}{3} \right)=\frac{2}{3}\] |
| \[\because \]\[\frac{1}{60}\]part is now filled in 1 min. |
| \[\therefore \]\[\frac{2}{3}\]part is now filled in \[=60\times \frac{2}{3}=40\min \] |
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