How many Mondays would there be in 171 school days?

There are 5 days to a school week: Monday, Tuesday, Wednesday, Thursday and Friday.

Divide number of school days by 5 to find the number of weeks:

171 / 5 = 34.2 weeks.

The weeks start with Monday, so there would be 35 Mondays. (34 full weeks and the partial week would begin with a Monday)

Divide 171 by 7 (as there are 7 days in each week), obtaining 24.4. There's one Monday in every 7 days, so in 168 days there'd be exactly 24 Mondays, and in 171 days there'd still be exactly 24 Mondays, with 3 days left over.