In a committee, 50 people speak French, 20 speak Spanish and 10 speak both Spanish and French. The number of persons speaking at least one of these two languages is:
Answer: B
Let F be the set for French speakers and S for Spanish speakers.
n(F) = 50, n(S) = 20, n(F ∩ S) = 10.
The number of people speaking at least one language is the union of the sets, n(F ∪ S).
n(F ∪ S) = n(F) + n(S) - n(F ∩ S) = 50 + 20 - 10 = 60.