Question

A boat travels 8 miles upstream in the same amount of time it can travel 12 miles downstream. In still water the speed of the boat is 5 mi/h. What is the speed of the current?

Answer 1

1 mi/hr

Explanation:

Given that:

Speed in still water, s = 5 mi/hr

Let speed of current = x

Time = distance /speed

Upstream (subtract speed of current) = 5 - x

Upstream time = 8 / 5 - x - - - (1)

Downstream (add speed of current) = 5 + x

Downstream time = 12 / 5 + x - - - (2)

Equate (1) and (2)

8 / (5 - x) = 12/ (5 + x)

8(5 + x) = 12(5-x)

40 + 8x = 60 - 12x

40 - 60 = - 12x - 8x

-20 = - 20x

x = 1

Spwed of current = 1 mi/hr