2007 AMC 12B Problems/Problem 10

Problem

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?

$\mathrm {(A)} 4$ $\mathrm {(B)} 6$ $\mathrm {(C)} 8$ $\mathrm {(D)} 10$ $\mathrm {(E)} 12$

Solution

First, determine the total number of people in the group.

$2=(40/100-30/100)t$

$t=200/10=20$

Now find the original number of girls:

$40/100t = 800/100 = 8$

So, there are 8 girls, $\Rightarrow \fbox{C}$

2007 AMC 12B (Problems • Answer Key • Resources)
Preceded by Problem 9	Followed by Problem 11
1 • 2 • 3 • 4 • 5 • 6 • 7 • 8 • 9 • 10 • 11 • 12 • 13 • 14 • 15 • 16 • 17 • 18 • 19 • 20 • 21 • 22 • 23 • 24 • 25
All AMC 12 Problems and Solutions

Page

Toolbox

Search

2007 AMC 12B Problems/Problem 10

Problem

Solution

See Also