1. Defining one variable in terms of another variable
Using only one variable, define each group.
boys in terms of girls
vs.
girls in terms of boys
15 Girls
5 Boys

2. There are 10 more girls than boys in the class.
X=# of boys
Therefore # of girls = x + 10

3. The number of girls in the class is three times as large as the number of boys.
X = # of boys
Therefore # of girls = 3x

4. The number of boys in the class is one-third of the number of girls.
X = # of girls
Therefore # of boys = 1/3 * x

5. Ten less than the number of girls in the class yields the number of boys.
X = # of girls
Therefore # of boys = x - 10