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.)

Jason - 9.375 miles per hour

Kevin -7.875 miles per hour

Step-by-step 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

not only in mathematics, scientific proof also are required in the other field of science. also maths proofs are of particular structure, containing steps and logics. so proving is like doing science, it is science. that's why it is important to prove. 

an inaccurate proof leads to errors, or stating results that are not accurate.  which wil mess the probelm up you dont want this