Seventy pupils (37 boys and 33 girls) are divided into two groups, with 40 pupils in Group 1 and 30 pupils in Group 2.
What is the difference between the number of boys in Group 1 and the number of girls in Group 2?
If you liked this problem, here is an NRICH task
which challenges you to use similar mathematical ideas.
This problem is taken from the UKMT Mathematical Challenges.