Question

Traveling with the wind, Jerry takes 10 minutes to bicycle to a local library 2.5 km away. Coming back against the wind, it takes him 15 minutes. What is Jerry's bicycling speed in still air?

Answer 1

7.5 km/h

Step-by-step explanation:

Let's assign the speed of Jerry in still air as x (in km/h)

Let's assign the speed of the wind as y (in km/h)

With the wind as Jerry’s back, he takes 10 minutes to get to the library. We can create the following equation. (we are converting the minutes to hours by dividing by 60);

2.5 / (x + y) = 10/60

10x + 10y = 150

x + y = 15

With the wind against Jerry, he takes 15 minutes from the library. We can create the following equation;

2.5 / (x-y) = 15/60

15x – 15y = 150

x – y = 10

We can now solve the simultaneous equation by subtraction;

x + y = 15

x – y = 10

2y = 5

y = 5/2 = 2.5

y = 2.5 km/h

x = 7.5 km/h

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