You should draw a Venn diagram first then solve the Unknowns using silmutaneous equations.
in a coaching centre of 70 but 4 students went on a university visit. 31 went to unilag, 35 went to lasu, and 36 went to u.i. 10 went to all the 3 universities. 12 went to unilag only, 13 went to lasu only, 15 went to u.i only. how many students visited...
1 - unilag and lasu
2 - at least 2 universities
3 - exactly 2 universities
4 - u.i or unilag but not lasu