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

Answer:

(C) 18

Step-by-step 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!