The boat floated downstream from one pier to another at a speed of 6.0 m / s, and back at a speed of 4.0 m / s.

The boat floated downstream from one pier to another at a speed of 6.0 m / s, and back at a speed of 4.0 m / s. Determine the average speed of the boat along the entire journey

V1 = 6 m / s
V2 = 4 m / s
S1 = S2 = S – the distance traveled by the boat in the forward and reverse directions is the same
Vav -?
Vav = (S1 + S2) / (t1 + t2)
Vav = (S1 + S2) / (S1 / V1 + S2 / V2)
Vav = (S + S) / S (V2 + V1) / V1 * V2
Vav = 2 * S * V1 * V2 / S (V2 + V1), the distance S in the numerator and denominator are reduced
Vav = 2 * V1 * V2 / (V2 + V1)
Vav = 2 * 6 * 4 / (6 + 4) = 4.8 m / s