Question 979609
Since you know that for every 3 boys there are 5 girls, you can multiply the numbers by a common number and the ratio will stay the same. I will multiply by 2:
 
{{{3:5}}}
{{{6:10}}}
 
In the ratio 6:10 there are 4 more girls than boys, let me try again.
 
{{{6:10}}}
{{{12:20}}}
 
There are now 8 more girls than boys, so you know there are 32 pupils in the class.