2007 AMC 10B Problem 14

Problem 14 of 25IntermediateAlgebra Arithmetic

Some boys and girls are having a car wash to raise money for a class trip to China. Initially

40\%

of the group are girls. Shortly thereafter two girls leave and two boys arrive, and then

30\%

of the group are girls. How many girls were initially in the group?

Show solution

Solution

Two girls leave and two boys arrive, so the group size is unchanged. The two girls who left therefore represent

40\%-30\%=10\%

of the group. Thus the group has

2\div 0.10=20

people, and the original number of girls was

40\%

20,

8.

Thus, the correct answer is C.

Tagged: percentage · linear equation