17. In a group of 48 children, the ratio of boys to girls is $3: 5$.
How many boys must join the group to make the ratio of boys to girls $5: 3$ ?
A 48
B 40
C 32
D 24
E 8
17. C Initially there are 48 children of whom $\frac{3}{8}$ are boys and $\frac{5}{8}$ are girls, so there are 18 boys and 30 girls. When more boys join, there are still 30 girls but now they form $\frac{3}{8}$ of the total. So the total number of pupils is now $\frac{8}{3} \times 30=80$, of whom $80-30=50$ are boys. Hence the number of boys joining is $50-18=32$.