Kari and Mona are looking at who in their class they have beaten at arm wrestling. Kari has beaten 15, wheras Mona has beaten 13. Of these, 7 have been beaten by both Kari andMona.

(a) Howmany have been beaten by at least one of them?

(b) Call the set of classmates beaten by Kari, K, and the set beaten by Mona M. How do you write the set of those who were beaten by both Kari and Mona?

(c) How do you write the set of those who were beaten by at least one of Kari or Mona?

(d) Recall that the cardinality (size) of the set A is |A|. Write a formula to link the cardinalities of the sets in the previous two exercises and those of M and K themselves.