Question

A man goes downstream with a boat to some destination and returns upstream to his original place in 5 hours. If the speed of the boat in still water and the stream are 10 km/hr and 4 km/hr respectively, the distance of the destination from the starting place is

• A. 16 km
• B. 18 km
• C. 21 km
• D. 25 km

Answer 1

Answer:

B. 18 km

Let the distance of the destination from the starting point be x km.

Rate downstream= (10 + 4) kmph = 14 kmph

Rate upstream = (10 – 4) kmph = 6 kmph

According to the question,

$\frac{x}{14}+\frac{x}{6}=5$

$\frac{3x+7x}{42}=5$

$10x=5\times{42}$

$x=21km$