Question

Melanie is 2 years older than her brother Tim. Ryan is 5 years younger than Melanie. If the sum of their ages is 56, how old is Melanie?

Answer 1

Setting variables

 Melanie's age: X

Tim's age: Y

Ryan's age: Z

Melanie is 2 years older than her brother Tim.

$X=2+Y$

Tim's age expression

$Y=X-2$ Equation (1)

Ryan is 5 years younger than Melanie.

$Z=X-5$ Ecuation (2)

 the sum of their ages is 56

$X+Y+Z=56$ Equation (3)

Replacing equation (1) and (2) in equation (3) and solving the equation for X

$X+X-2+X-5=56\\ 3X-7=56 \\ 3X=56+7\\ 3X=63\\ X=\frac{63}{3}\\ X=21$

Melanie is $\boxed{21 \text{years old}}$