We can use PIE, (Principle of Inclusion - Exclusion)

We can add 48 + 39 + 35 = 122, but this is over counting since some people took 2 or even 3 classes.

From 122, we need to subtract 20 + 19 + 22 = 61.

But we need to add 10 back to count the ones who took all the classes.

61 + 10 = 71.

100 - 71 = 29

29 students did not enroll in any of the subjects.