Question

Dodi bicycles 14mph with no wind. Against the wind, Dodi bikes 10mi in the same time it takes to bike 20mi with the wind. What is the speed of the wind?

Answer 1

4.67 mph

Explanation:

Speed with no wind = 14 mph

Let wind speed = w mph

Thus;

Speed with wind = 14 + w

Speed against the wind = 14 - w

Now, we are told that against the wind he bikes 10 miles.

Thus, from; time = distance/speed, we have;

Time = 10/(14 - w)

Also, we are told he biked 20 miles with the wind. Thus;

Time = 20/(14 + w)

We are told the times he used in both cases are the same.

Thus;

10/(14 - w) = 20/(14 + w)

Divide both sides by 10 to get;

1/(14 - w) = 2/(14 + w)

Cross multiply to get:

1(14 + w) = 2(14 - w)

14 + w = 28 - 2w

w + 2w = 28 - 14

3w = 14

w = 14/3

w = 4.67 mph