Question

A boatman goes 2 km against the current of the stream in 1 hour and goes 1 km along the current in 10 minutes. How long will it take to go 5 km in stationary water?

• A. 40 minutes
• B. 1 hour
• C. 1 hr 15 min
• D. 1 hr 30 min

Answer 1

The correct option is C 1 hr 15 min

Rate downstream $=(\frac{1}{10}\times 60)km/hr=6km/hr$
Rate upstream = 2 km/hr
Speed in still water $=\frac{1}{2}(6+2)km/hr=4km/hr$
$\therefore$ Required time $=\left(\frac{5}{4}\right)hrs=1\frac{1}{4}hrs=1hr.15min$