Question

A Viking ship can travel 25 miles against a current in the same time that it can travel 50 miles with the current. The rate of the current 2.5 miles per hour. Which of the following is the rate of the ship in still water

Answer 1

7.5 miles per hour

Explanation:

distance = rate × time

time = distance / rate

If x is the rate of the ship in still water, then x + 2.5 is the rate with the current, and x − 2.5 is the rate against the current.

The time to go 25 miles against the current is the same as the time to go 50 miles with the current.

t = t

d / r = d / r

25 / (x − 2.5) = 50 / (x + 2.5)

Cross multiply.

25 (x + 2.5) = 50 (x − 2.5)

Simplify and solve.

25x + 62.5 = 50x − 125

187.5 = 25x

x = 7.5