+75 Of the 30 students in my class, 11 practice taekwondo, 11 play piano, and 20 take lessons at MS. 4 students play piano and go to MS, 3 students do taekwondo and play piano, 5 students go to MS and practice taekwondo, and 3 students do none of these. How many students do all 3?
+605 The problem is trivialized by https://en.wikipedia.org/wiki/Inclusion%E2%80%93exclusion_principle.
