17. There are six more girls than boys in Miss Spelling's class of 24 pupils. What is the ratio of girls to boys in this class?
A $5: 3$
B $4: 1$
C $3: 1$
D $1: 4$
E $3: 5$
Solution: $\mathbf{A}$
Suppose there are $g$ girls and $b$ boys in Miss Spelling's class. As there are 6 more girls than boys, $g-b=6$. As there are 24 pupils altogether, $g+b=24$. Adding these equations gives $2 g=30$, so $g=15$. Hence $b=15-6=9$. So the ratio $g: b$ is $15: 9$ which is the same as $5: 3$.