The speed of a boat in still water is 20 mph. It travels 24 mi upstream and 24 mi downstream in a total time of 10 hr. what is the speed if the current?

Answer 1

Recall that speed is distance traveled over time:
v = d/t

Represent the unknowns:
Let x = speed of current
Let t = time upstream
Let 10-t = time downstream (since the total time is 10 hours according to the problem)
Note that when the boat travels upstream, the current is against it, so the speed of boat is decreased), while if it travels downstream, the current has the same direction of flow as the boat, so its speed is increased.
The distance traveled in upstream and downstream are the same. We can now write the equations for distance traveled for upstream and downstream:
upstream: 24 = (20 - x)t
downstream : 24 = (20 + x)(10 - t)
You have two equations and two unknowns, so you can now solve for the unknowns. You can use substitution method to find x and t.

hope this helps~ `u`