A motor boat can row at the speed of 12 km/h in still water. If the river is flowing at 4 km/h and it takes 12 hours for a round trip, then the distance between the two places is :
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 64 km
Going with the stream the speeds add; going against it they subtract.
\(\text{Downstream speed} = 12 + 4 = 16 \text{ km/h}\)
\(\text{Upstream speed} = 12 - 4 = 8 \text{ km/h}\)
Let the distance be d km. The round trip takes 12 hours:
\( \displaystyle \frac{d}{16} + \frac{d}{8} = 12 \)
\( \displaystyle \frac{3d}{16} = 12 \)
\(d = 64\)
The distance between the two places is 64 km.