A boat traveling upstream goes 84 kilometers in 7 hours. If the return trip takes only 3 hours, what is the speed (in kilometers per hour) of the boat still in water?

Respuesta :

Speed = Distance ÷ time 

Speed upstream = 84 ÷ 7 = 12 km/h

Speed downstream = 84 ÷ 3 = 28 km/h

Speed in still water = 1/2(28 + 12) = 20 km/h

Answer: 20 km/h