Question

Julie and Eric row their boat (at a constant speed) downstream for 40 miles in 4 hours, helped by the current. Rowing at the same rate the trip back, against the current, takes 10 hours. Find the rate of the current.

Answer 1

Answer: 3 miles per hour

Explanation:

Use the formula "distance (d) = rate (r) x time (t)" to create a system of equations.

Let "r" represent the rate they are rowing

Let "c" represent the current

time rate distance EQUATION

Downstream: 4 hours r + c 40 miles 4(r + c) = 40

Upstream: 10 hours r - c 40 miles 10(r - c) = 40

Distribute, then eliminate r to solve for c:

Down: 4r + 4c = 40 → 5(4r + 4c = 40) → 20r + 20c = 200

Up: 10r - 10c = 40 → -2(10r - 10c = 40) → -20r + 20c = -80

40c = 120

÷40 ÷40

c = 3