Question

A Preschool class has 3-year olds and 4-year olds. There are 17 children in the class, and the total of their ages is 63. Which system of linear equations represents the problem

Answer 1

(3x) + (4y) = 63
x+ y = 17

Answer 2

By substitution...
(3*(17-y))+(4y) = 63
51-3y+4y=63
y=63-51
y=12

Answer 3

Since x+y=17, for y=12 we have x=5.
X represents the number of 3 year olds and y represents 4 year olds