Question

The number of girls in Mrs. Manning’s classes was 12 less than twice the number of boys. She had a total of 108 students in her classes. How many girls and how many boys are in Mrs. Manning’s classes?

Answer 1

40 boys and 68 girls

let's start with variables and an equation.

boys: x

girls: 2x - 12

and we know that boys and girls make up the class. so let's add the two expressions.

x + 2x - 12 = 108

3x - 12 = 108

    + 12     + 12

3x = 120

x = 40 boys

BUT x is only the number of BOYS in the class. so we have to find girls now. let's plug in our value of x into the girls' equation.

2x - 12 = # of girls

2(40) -12 = # of girls

80 - 12 = # of girls

68 girls

let's check our answer!

68 + 40 does in fact add to 108, therefore our answer is correct.