In a committee, 50 people speak French, 20 speak Spanish, and 10 speak both Spanish and French. How many speak at least one of these two languages?

Let F be the set of people in the committee who speak French, and S be the set of people in the committee who speak Spanish.
∴n(F)=50,n(S)=20,n(S∩F)=10
We know that:
n(S∪F)=n(S)+n(F)-n(S∩F)=20+50-10=60
Thus, 60 people in the committee speak at least one of the two languages.