Question

Haji rows his canoe 10 mph in still water. He noticed one day that he could row 4 miles upstream in the same amount of time he could row 6 miles downstream. What was the approximate speed of the current that day?
2.0 mph
3.3 mph
5.0 mph
10.0 mph

Answer 1

Let c be the current speed. Upstream speed = 10 − c, downstream = 10 + c.
Set times equal: 4/(10 − c) = 6/(10 + c).
Solve: 4(10 + c) = 6(10 − c) → 40 + 4c = 60 − 6c → 10c = 20 → c = 2 mph.

Answer: 2.0 mph.