Question

kelsey is kayaking on a river. she travels 5 miles upstream and 5 miles downstream in a total of 6 hours. i’m still water kelsey can travel at an average speed of 3 miles per hour. what is the average speed of the rivers current?

Answer 1

2mph

Explanation:

Kyle, d = rt, right? This means that t = d/r.

If we call the rate of the current c, then her rate upstream is hindered by the current and is 3 - c. Downstream is 3 + c.

The total time is 6 hours...

5/(3 - c) + 5/(3 + c) = 6

Once we put everything over the same denominator, we don't need it anymore.

5(3 + c) + 5(3 - c) = 6(3 - c)(3 + c)

15 + 5c + 15 - 5c = 54 - 6c2

30 = 54 - 6c2

6c2 = 24

c2 = 4

c = 2

2 mph