Question

A boat goes downstream and covers the distance between two ports in 4 hours, while it covers the same distance upstream in 5 hours. If the speed of the stream is 2 km/hr, find the speed ofboat in still water.

• A. 16 km/hr
• B. 18 km/hr
• C. 20 km/hr
• D. 15 km/hr

Answer 1

The correct option is B 18 km/hr

Let the distance between two port be ${}^{\prime }{x}^{\prime }$ km.

And speed of boat in still water be ${}^{\prime }{S}^{\prime }$ km/hr.

According to question,

In downstream,

$x=(S+2)$x4 ........(1) as, (Distance= Speed x Time)

Similarly,

In upstream,

$x=(S-2)$x5 ........(2)

From (1) & (2),

$(S+2)4=(S-2)5$

=> $4S+8=5S-10$

=> $S=18$ km/hr.