If the speed of the motor boat in still water is 24 km/hr. It takes thrice as long as to go downstream to a place as to return downstream to the starting place, then speed of the stream is _____________.
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → 12 km/hr
Let the speed of the motorboat in still water be 24 km/hr, and speed of stream be x km/hr.
Downstream speed = $(24+x)$ km/hr
Upstream speed = $(24-x)$ km/hr
$\frac{\text{Distance}}{\text{Upstream Speed}}=3×\frac{\text{Distance}}{\text{Downstream Speed}}$
$\frac{1}{24-x}=3×\frac{1}{24+x}$
$⇒4x=48$
$⇒x=12$ km/hr