Question

A fourth grade class has 20 students. The number of girls is 7 less than twice the number of boys. How many boys are in the class?

Answer 1

Answer: There are 9 boys.

Explanation

To solve this problem, we have to build a system of two equations, using b to represent the boys and g to represent the girls, we can translate the sentence into an algebraic expression.

• Equation 1: ",A fourth-grade class has 20 students":

$b+g=20$

• Equation 2: ",The number of girls is 7 less than twice the number of boys.":

$g=2b-7$

To solve, we can replace the expression for g (Equation 2), into the Equation 1 and solve for b:

$b+(2b-7)=20$$b+2b-7=20$$3b-7=20$$3b=20+7$$3b=27$$b=\frac{27}{3}$$b=9$

Thus, there are 9 boys.