Find Frank’s approximate speed in still water.

Question

Frank rows 10 km upstream and 10 km back in a total time of 3 hours. If the speed of the
river is 5 km/h, then find Frank’s approximate speed in still water.

Answer 1

v = Frank's speed in still water = ?

w = speed of current = 5 km/h

d = one-way distance = 10 km

total travel time = 3 h

 

Upstream:

 

t = d/(v - w) = 10/(v - 5)

 

Downstream:

 

3 - t = d/(v + w) = 10/(v + 5)

 

Add these 2 equations and get

 

3 = 10/(v -5) + 10/(v + 5)

 

Can you solve for v and finish from here?