Question

Kevin and his elder brother Jason jog every morning. Kevin runs 1.5 miles per hour slower

than Jason. When Jason ran 5 miles, Kevin only ran 4.2 miles. Find their running speeds.
(Write an algebraic equation first, then solve.)

Answer 1

Jason - 9.375 miles per hour

Kevin -7.875 miles per hour

Explanation:

Let Jason’s running speed be x miles per hour

Kevin runs 1.5 miles per hour less;

so his running speed will be (x-1.5) miles per hour

At any point, distance = speed * time

Their running time is same here;

Jason’s running time will be 5/x

Kevin’s running time will be 4.2/(x-1.5)

These times are equal;

So;

5/x = 4.2/(x-1.5)

5(x-1.5) = 4.2x

5x - 7.5 = 4.2x

5x-4.2x = 7.5

0.8x = 7.5

x = 7.5/0.8

x = 9.375 miles per hour

So kevin’s speed will be 9.375 - 1.5 = 7.875 miles per hour