Question

A boy rows a boat against a stream flowing at 2 kmph for a distance of 9 km, and then turns round and rows back with the current. If the whole trip occupies 6 hours, find the boy’s rowing speed in still water.

• A. 4 kmph
• B. 3 kmph
• C. 2 kmph
• D. 5 kmph

Answer 1

Answer:

A. 4 kmph

Let the speed of rowing be X.

Speed of Stream is 2 kmph.

Then the equation formed is,

$\frac{9}{X-2}+\frac{9}{X+2}=6$

$\frac{9(X+2)+9(X-2)}{X^2-2^2}=6$

$\frac{9X+18+9X-18}{X^2-4}=6$

$18X=16(X^2-4)$

$9X=8(X^2-4)$

$8X^2-9X-32=0$

On solving, we get the value of X as 4.