Question

A boat can go $65km$ upstream in $5$ hours and $69km$ downstream in $3$ hours. Find the speed of boat in still water.

• A. $12km/hr.$
• B. $18km/hr.$
• C. $16km/hr.$
• D. $21km/hr.$

Answer 1

The correct option is B $18km/hr.$

It is given that boat can go $65$ km upstream in $5$ hours that is:

Upstream speed$=\frac{65}{5}=13$ km/hr

Also, the boat can go $69$ km downstream in $3$ hours

Downstream speed $=\frac{69}{3}=23$ km/hr

We know that Speed in still water$=\frac{1}{2}(upstreamspeed+downstreamspeed)$ km/hr

Speed in still water $=\frac{1}{2}(13+23)=18$ km/hr

Hence, the speed of boat in still water is $18$ km/hr.