Sunil’s boat moves at 9 km/hr in still water, and the river flows at 1 km/hr. He goes up the river from his house to a temple and then comes back. Going to the temple takes him 1 hour 30 minutes more than coming back. How far is the temple from his house?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → 60 km
The temple is up the river, so going there is against the river and coming back is with it. The going time minus the coming-back time is 1 hour 30 minutes, that is 1.5 hours.
Let the distance be \(d\) km
Upstream speed \(=9-1=8\) km/hr, downstream speed \(=9+1=10\) km/hr
\(\displaystyle \frac{d}{8}-\frac{d}{10}=1.5\)
\(\displaystyle \frac{5d-4d}{40}=1.5\), so \(d=60\) km
Check: \(60\div8=7.5\) hr going and \(60\div10=6\) hr back; the difference is 1.5 hr