Jessica can bike an average of 15 mph without wind. One day, Jessica does a 20 mile ride against the wind in the same time that she does a 40 mile ride with the wind. What is the speed of the wind?

Answer: the speed of the wind is 5mph

Step-by-step explanation:

Let x represent the speed of the wind.

Jessica can bike an average of 15 mph without wind. One day, Jessica does a 20 mile ride against the wind in the same time that she does a 40 mile ride with the wind. This means that her total speed against the wind is (15 - y) mph and her total speed with the wind is (15 + y) mph.

Time = speed * time

Time spent in travelling against the wind is

20 / (15 - y)

Time spent in travelling with the wind is

40 / (15 + y)

Since the time is the same, it means that

20 / (15 - y) = 40 / (15 + y)

Cross multiplying, it becomes

40 (15 - y) = 20 (15 + y)

600 - 40y = 300 + 20y

20y + 40y = 600 - 300

60y = 300

y = 300/60

y = 5 mph