Question

A boat can go $72km$ downstream in $4$ hours and $36km$ upstream in $3$ hours. Calculate the speed of boat in still water.

• A. $15km/hr$
• B. $12km/hr$
• C. $18km/hr$
• D. $24km/hr$

Answer 1

The correct option is A $15km/hr$

It is given that boat can go $72$ km downstream in $4$ hours that is:

Downstream speed $=\frac{72}{4}=18$ km/hr

Also, the boat can go $36$ km downstream in $3$ hours

Upstream speed $=\frac{36}{3}=12$ km/hr

Speed in still water $=\frac{1}{2}(18+12)=15$ km/hr

Hence, the speed of boat in still water is $15$ km/hr.