In a still lake, a boating team can row their boat at speed of 10 km an hour. They enter a river flowing at 5 km an hour. Travelling downstream in how much time can they expect to cover distance of 30 km ?

2 hrs

The correct answer is Option (3) → 2 hrs

$\text{Time}=\frac{\text{Distance}}{\text{Speed}}$

Speed downstream = 10 + 5 = 15 km/hr

Time = $\frac{30}{15}=2$ hours