Question

While on vacation, Kevin went for à swim in a nearby lake. Swimming against the current, it took him 8 minutes to swim 200 meters. Swimming back with the current took half as long. What is his and the lake's current average speed?

Answer 1

Kevin's speed is 37.5 meters per minute. Lake's current has a speed of 12.5 meters per minute.

Explanation:

You have two equations and two unknowns.

Let me assign k as Kevin's speed and c as the speed of current.

`k-c = 25` because it takes 8 minutes to swim 200 meters against the current (`200/8=25` meters per minute).

`k+c = 50` because it takes 4 minutes to swim 200 meters when he swims on the same directions of the current (`200/4 = 50` meters per minute).

When you add these two equations:

`k-c + k+c = 25+50`

`2timesk = 75` and

`k=37.5` meters per minute.

Put this value into any equation provided abobe

`k-c = 25`

`37.5-c = 25`

`37.5 - 25 = c = 12.5` meters per minute.

Kevin's speed (in water) is 37.5 meters per minute and current speed is 12.5 meters per minute.