Question

Michelle is 7 years older than her sister Joan, and Joan is 3 years younger than their brother Ryan. If the sum of their ages is 64, how old is Joan?

16
22
18
19

Answer 1

(C) 18

Explanation:

We can create a systems of equations. Assuming
`m` is Michelle's age,
`j` is Joan's age, and
`r` is Ryan's age, the equations are:

`m = j + 7`

`j = r-3`

`m+j+r = 64`

We can use substitution, since we know the "values" of m and j.

`(j+7)+(r-3)+r = 64\\(j+7)+(2r-3)=64\\2r + j + 4 = 64\\2r + j = 60\\\\`

`r = 21, j = 18`

So we know that Joan is 18 years old.

Hope this helped!