<PRE><B>Question 477900</B>
&lt;p&gt;Set B for the number of boys on the first day. Set G for the number of girls.

so {{{B+G=A}}} (A for all), where {{{B=.6A}}} (sixty percent).&lt;/p&gt;

&lt;p&gt;Six girls move
{{{G-6}}}&lt;/p&gt;

&lt;p&gt;and six boys come
{{{B+6}}}&lt;/p&gt;

&lt;p&gt;And now the boys make up 75% of the class
{{{B+6=.75A}}}&lt;/p&gt;

&lt;p&gt;Using {{{B=.6A}}} and {{{B+6=.75A}}}, plug in .6A for B:
{{{.6A+6=.75A}}}&lt;/p&gt;

&lt;p&gt;Subtract .6A from both sides:
{{{6=.15A}}}&lt;/p&gt;

&lt;p&gt;Now divide both sides by .15
{{{40=A}}}&lt;/p&gt;

&lt;p&gt;So there were 40 kids in all on the first day. 60% of them were boys, so:
{{{.6(40)=B}}}
{{{24=B}}}&lt;/p&gt;

&lt;p&gt;40-24=G
{{{G=16}}}&lt;/p&gt;

So on the first day of school, there were 24 boys and 16 girls.</PRE>