Let the numbers be ‘a’ and ‘b’.

Given, sum of two numbers is 8. If their sum is four times their difference, find the number.

⇒ a + b = 8 ------ (1)

Also,

a + b = 4(a – b)

⇒ a + b = 4a – 4b

⇒ a = 5b/3

Substituting value of a in eq1

⇒ 5b/3 + b = 8

⇒ 8b/3 = 8

⇒ b = 3

Thus, a = 5