Question

Mark (✓) against the correct answer
If $\frac{4}{5}$ of a cistern is filled in 1 minute, how much more time will be required to fill the rest of it?

(a) 20 seconds
(b) 15 seconds
(c) 12 seconds
(d) 10 seconds

Answer 1

Time taken to fill $\frac{4}{5}$ of a cistern = 1 min
Time taken to fill 1 cistern $=\frac{5}{4}$ min
Time taken to fill $\frac{1}{5}$ of a cistern = $\frac{5}{4}\times \frac{1}{5}=\frac{1}{4}$ min = 15 seconds

Hence, it will take 15 seconds to fill the rest of the cistern.

Thus, the correct option is (b).