There are $$50$$ students in your class. The ratio of boys to girls is $$2:3$$. How many boys and girls are there? 
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According to the ratio $$2:3$$, we could know the total is $$5$$. Then the number of boys is $$50\times\frac{2}{5}=20$$. The number of girls is $$50\times\frac{3}{5}=30$$. 