Question

Sophie is the oldest of three siblings whose ages are consecutive integers. If the sum of their ages is 51, find Sophie's age.

Answer 1

Let Sophie's age be x. The other two are x−1 and x−2.
x + (x−1) + (x−2) = 51 ⇒ 3x − 3 = 51 ⇒ 3x = 54 ⇒ x = 18.

Sophie is 18 years old.