What fraction is $\frac{2}{5}$ of $\frac{3}{4}$?

Question

$\frac{2}{5}$ of blood donors at a centre have group O blood. $\frac{3}{4}$ of these donors are under 30. What fraction of the group O blood donors at the centre are under 30?

What I did was divide $\frac{2}{5}$ by $\frac{3}{4}$ to get $\frac{8}{15}$. Am I heading in right direction or completely off?

Answer 1

EDIT: As @TonyK pointed out, this answer is incorrect. See @TonyK's answer for why that is. I'll leave my own response here for reference.

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You need the fraction of people who $$ \Big(\text{have group O blood}\Big) \mathbf{AND} \Big(\text{are under 30}\Big) $$

This "AND" translates to multiplication, so the fraction of the group O blood donors at the centre that are under 30 would be

$$ \Big(\text{fraction that have group O blood}\Big) \times \Big(\text{fraction that are under 30}\Big) $$ }

Answer 2

This is a bit of a trick question. Assuming that age and blood group are not correlated, the fraction of group O blood donors that are under 30 is the same as the fraction of all blood donors that are under 30: $3/4$.