A boat covers a distance 24 km upstream and returns to the same point in a total of 4 hours. If the speed of boat in downstream is twice its speed in upstream, then the speed of boat in upstream is:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 9 km/h
Let speed of boat in upstream = $x$ km/h.
Then speed of boat in downstream = $2x$ km/h.
Time taken upstream = $\frac{24}{x}$
Time taken downstream = $\frac{24}{2x} = \frac{12}{x}$
Total time = $\frac{24}{x} + \frac{12}{x} = \frac{36}{x}$
Given total time = 4 hours
$\frac{36}{x} = 4$
$x = \frac{36}{4} = 9$
Therefore, speed of boat in upstream = $9 \, \text{km/h}$