A log floats 12 km down a river in 4 hours. A boat that moves at 10 km/h in still water goes 26 km downstream on the same river. How long does it take?

Explanation

1. 01

   A floating log moves at the stream's speed: $\frac{12}{4} = 3$ km/h.

2. 02

   Downstream speed $10 + 3 = 13$ km/h, so $\frac{26}{13} = 2$ hours.