Question

It takes 2 hours for a boat to travel 28 miles downstream.The same boat can travel 18 miles upstream in 3 hours .Find the rate of the stream's current.

Answer 1

4 mph

Explanation:

The speed downstream is (28 mi)/(2 h) = 14 mph.

The speed upstream is (18 mi)/(3 h) = 6 mph.

The speed of the current is half the difference of these:

(14 mph -6 mph)/2 = 4 mph

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The current adds to the downstream speed and subtracts from the upstream speed, so the difference of those speeds is twice the current's speed.