Twice the difference between two numbers is equal to their sum. If one number is 15, find the other number.

Let the numbers be x and y

From the given data, we get

⇒ 2 (x – y) = x + y

Given that one number x = 15

⇒ 2 (15 – y) = 15 + y

⇒ 30 – 2y = 15 + y

⇒ 15 = 3y

⇒ y = 5