South African Mathematics Olympiad Second Round

For convenience assume there are $300$ learners, i.e. $200$ girls and $100$ boys.

$30\%$ of $200$ is $60$ and $45\%$ of $100$ is $45$.

Thus, $60+45=105$ learners have completed their project.

The percentage of learners who still need to complete their project is thus $$\frac{300-105}{300}\times 100=\frac{195}{3}=65.$$