Question

the sum of the ages of John and his sister is 60. Two years ago, John's sister was three times as old as John. Calculate John's age and the age of John's sister when he was born.
I just want to know the formulas and the answer. plz, I need your help.​

Answer 1

Step-by-step explanation:

Let A(B) denote the age of brother.

Let A(S) denote the age of his sister.

Given: A(B) = A(S) + 12, and

A(B) = 3 * A(S);

One can use the idea that, two things that are equal to the same thing are equal to each other:

A(B) = A(S) + 12, equation (1)

A(B) = 3 * A(S), equation (2)

Remembering that two things equal to the same thing are equal to each other, we have equation (1) = equation (2), that is:

A(S) + 12 = 3 * A(S), subtracting A(S) from both sides one gets 12 = 2 * A(S). Now dividing both sides by 2 we get A(S) = 12/2 = 6 . Therefore, the age of the sister is 6 years when her brother John is three times as old, that is 18 years.