Question 95505
Let x=size of class before the 12 boys join

Then x+12 =size of class after the 12 boys join


Now we know that the total number of girls in the class before the 12 boys are added equals the total number of girls in the class after the 12 boys are added.  So, we have:

(3/4)x=1/2(x+12)  myltiply each term by 4
3x=2(x+12) get rid of parens

3x=2x+24  subtract 2x from both sides
3x-2x=2x-2x+24  collect like terms

x=24-------------------size of class before the 12 boys are added

x+12=24+12=36--------------------------size of class after the 12 boys are added

CK

(3/4)*24=18

18=1/2 of 36


Hope this helps-----ptaylor