Question 327487
On the first day of school, the percentage of boys in a particular class is 60%.
 During the school year, six girls move away, and are replaced in the class by six boys; this makes the class roster 75% boys.
 Find the number of boys and girls in the class on the first day of school. 
:
Let x = no. in the class on the 1st day of school
then
.6x = no. of boys on the 1st day
and
.4x = no. of girls on the 1st day
:
.75x = .6x+6 
.75x - .60x = 6
.15x = 6
x = {{{6/.15}}}
x = 40 is the no. on the 1st day of school
:
:
Check solution by using the no. of girls
.25x = .4x - 6
.25x - .4x = 6
.15x = 6 
 x = 40, confirms our solution of 40 students