Question

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

• A. $1$ hour
• B. $1\frac{1}{2}$ hours
• C. $1$ hour $15$ min
• D. $40$ min

Answer 1

The correct option is C $1$ hour $15$ min

Speed of the boatman upstream = $\frac{2}{1}$ km/hr = 2 km/hr
Speed of the boatman downstream = $\frac{1}{\frac{10}{60}}$ km/hr = 6 km/hr
$\therefore$ Speed of boatman in stationary water = $\frac{1}{2}(6+2)$ km/hr = 4 km/hr
$\therefore$ Time taken to cover 5 km in stationary water = $\frac{5}{4}hrs=1\frac{1}{4}hrs$ = 1 hr 15 min