The raft sailed along the river in the first 2 hours – 18 km, in the second 3 hours – 27 km. Find the average speed along the river.

These tasks: the first part of the raft path (t1 = 2 h; S1 = 18 km); the second part of the raft path (t2 = 3 hours; S2 = 27 km).

The average speed of movement of the considered raft along the river (average speed of the current) is determined by the formula: Vav. = (S1 + S2) / (t1 + t2).

Let’s make a calculation: Vav. = (18 + 27) / (2 + 3) = 45/5 = 9 km / h.

Answer: The average speed of the raft (river flow) is 9 km / h.