In Miss Quaffley's class, one third of the pupils take a teddy bear to school.
Last term, each boy borrowed 12 books from the library, each girl borrowed 17 books, and each teddy bear borrowed 9 books.
In total 305 books were borrowed.
How many girls are there in the class?
If you liked this problem, here is an NRICH task
that challenges you to use similar mathematical ideas.