Question

A person swims 11 miles downstream in the same time they can swim 7 miles up stream. The speed of the current is 4 miles per hour.

These situations can be represented by the equations
Downstream: t=11/s+4 Upstream:t=7/s-4,
where t stands for time and s is the speed of the swimmer. What is the speed of the swimmer swimming in still water?

Answer 1

s = 18 mph

Explanation:

At downstream, time is; t = 11/(s+ 4)

At upstream, time is; t = 7/(s - 4)

Since they both are passed in the same time, then ;

11/(s+ 4) = 7/(s - 4)

Cross Multiply to get;

11(s - 4) = 7(s + 4)

11s - 44 = 7s + 28

11s - 7s = 44 + 28

4s = 72

s = 72/4

s = 18