The sum of ages of A and B is 12 years more than the sum of ages of B and C. Then C is how many years younger than A?

Let us assume the A age is P , B age is Q and C age is R years.
Sum of the age of A and B age is P + Q years and B and C ages is Q + R Years.
According to question,
The sum of ages of A and B is 12 years more than the sum of ages of B and C
Here, (P + Q) = (Q + R) + 12
⇒ (P + Q) - (Q + R) = 12
⇒ P - R = 12
∴ P = R + 12
Hance, C is 12 years younger than A.