The sum of Juan’s age and Sara’s age is 33 yrs. If Sara is 15 yrs old, how old is Juan?

The sum of Juan’s age and Sara’s age is 33 yrs. If Sara is 15 yrs old, how old is Juan?

Let j be Juan's age and s be Sara's age. We have the following equations:

1. j + s = 33
2. s = 15

Substitute (2) into (1)
j + 15 = 33

Using our equation solver, we get j = 18