It took a boat 6 h to travel 84 km up a river against the current but only 4 h and 12 minutes for the return trip with the current. Find the speed of the boat in still water and the speed of the current water.

Answer 1

Vb - Vw = 84km/6h = 14km/h.
Vb + Vw = 84km/4.2h = 20 km/h.

Eq1: Vb - Vw = 14
Eq2: Vb + Vw = 20
Add the Eqs:
2Vb = 34
Vb = 17 km/h. = Velocity of boat.

In Eq2, substitute 17 for Vb:
17 + Vw = 20
Vw = 3 km/h = Velocity of the water.