A river flows at 2 km per hour. Jakob and his friend row 16 kilometers upstream and 16 kilometers downstream to return. This trip takes them 6 hours.

Question

On average, in kilometers per hour, how fast are they rowing?

Answer 1

This problem actually has 3 unknowns, but there really are 3 equations!

Let B= boys' rowing rate

T_D=time down stream

T_u=time upstream.

(B+2)T_D=16 and (B-2)T_U=16, i.e.

T_D=16/(B+2) and T_U=16/(B-2)

T_D + T_U = 6

Plug the expressions for T_D and T_U into the above equation and solve the resulting quadratic equation for B.

Answer 2

So the flow of the river is a distraction. We can actually disregard that information. From the question, we know that Jacob and his friend row 16 km up then 16 km back down with a total of 6 hours. And we are asked to find km/hr. So we need to add the distance for the whole trip and then divide it by the total time for the trip to solve it.

1) add the 16 together. 16km + 16km =32km.

2) divide the total distance by the total hours. 32km/6 hrs

3) simplify. 6 can go into 32 5 times with a remainder of 2. So on average their speed is 5 1/3 or 5.33 km/hr.

Hope this help.