ILLUSTRATION 1

At the birthday party of Sherry, a baby boy, 40 persons chose to kiss him and 25 chose to shake hands with him. 10 persons chose to both kiss him and shake hands with him. How many persons turned out at the party?

(a) 35 (b) 75

(c) 55 (d) 25

SoL

Fromthe figure, it is clear that the number of people at the party were 30 + 10+15 = 55. We can of course solve this mathematically as below:

Let n(A) = No. of persons who kissed Sherry = 40

n(B) = No. of persons who shake hands with Sherry = 25 and n(A « B) = No. of persons who shookhands with Sherry and kissed him both =10

Then using the formula, n( A » B) = n( A) + n(B) - n( A « B)

n(A » B) = 40 + 25 - 10 = 55