A motorboat can travel 10 km against the stream in 30 minutes and returns back at the same point in 10 minutes. The speed of the stream is,
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → 20 km/hr
Against the stream (upstream) the boat covers 10 km in 30 minutes, and with the stream (downstream) it covers 10 km in 10 minutes:
\( \displaystyle \text{Upstream speed}=\frac{10}{1/2}=20\ \text{km/hr} \)
\( \displaystyle \text{Downstream speed}=\frac{10}{1/6}=60\ \text{km/hr} \)
The speed of the stream is half the difference of these two speeds:
\( \displaystyle \text{Speed of stream}=\frac{60-20}{2} \)
\( \displaystyle =20\ \text{km/hr} \)
CBSE Applied Mathematics (Class XII):
Boats and Streams
