Of the 50 entries in a costume contest, 31 entrants were dressed as heroes and 20 entrants were wearing a mask. if 9 entrants were dressed as heroes wearing a mask, how many entrants were neither dressed as heroes nor wearing a mask

8

Step-by-step explanation:

Given that Of the 50 entries in a costume contest, 31 entrants were dressed as heroes and 20 entrants were wearing a mask.  9 entrants were dressed as heroes wearing a mask.

Let A = heroes and B = wearing mask

n(U) = 50

n(A)=31 and n(B) = 20 and n(AB) =9

Hence n(AUB) =

Persons who were neither dressed as heroes nor wearing a mask