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
