In a class of $$40$$ pupils, there are $$10$$ more boys than girls.  What is the ratio of the number of girls to the number of boys? 
Overseas Competition->Knowledge Point->Calculation Modules->Ratios and Proportions->Ratio
Total people $=2u+10=40$  $2u=40-10=30$  Girls $=1u=30\div2=15$  Boys $=1u+10=15+10=25$  Girls $:$ Boys $\to$ $15:25$ $\to$ $3:5$ 