Some people just cannot resist temptation:

The burglar(s) did not appear to be out after material gain. Instead of stealing, the intruder(s) sat down and began to solve the math problems intended for third grade students, newspaper Adresseavisen reports.

According to local law enforcement officials a good job was done and all of the problems were solved correctly.

There has been nothing reported missing or stolen from the school building and it remains a mystery how the intruder or intruders gained access to the school.

I'm assuming the children are quite upset, being deprived of the opportunity to solve these problems for themselves.