Question

A rowing team rowed 90 miles while going with the current in the same amount of time as it took to row 10 miles going against the current. The rate of the

current was 4 miles per hour. Find the rate of the rowing team in still water.
Rate of the team in still water:
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Answer 1

The speed in still water is 5 miles per hour.

Explanation:

distance with current = 90 miles

distance against current = 10 miles

speed in still water = s

speed of current = 4 mph

speed with current = s + 4

speed against current = s - 4

time = t

speed = distance/time

distance = speed * time

With current:

90 = (s + 4) * t

Against the current:

10 = (s - 4) * t

We have a system of equations:

90 = (s + 4) * t

10 = (s - 4) * t

90 = ts + 4t

10 = ts - 4t

Subtract the second equation from the first equation.

80 = 8t

10 = t

t = 10

10 = t(s - 4)

10 = 10(s - 4)

1 = s - 4

s = 5

Answer: The speed in still water is 5 miles per hour.