EXAMPLE 3.4.3 SOLUTION

Since the data is given in terms of percentages, we will pretend that the total population of guests is 100.

 

1. If we identify those cells of the table corresponding to guests who either scream or punch or do both, we see that there are three such cells. The corresponding numbers are:

14 + 52 + 8 = 74. The probability is 74/100 = .74

 

We could also get the answer by using the formula P(A or B) = P(A) + P(B) - P(A and B).

 

P(screams or punches) = P(screams) + P(punches) - P(does both)

= .66 + .22 - .14 = .74

 

2. The condition "doesn't scream and doesn't punch" is the complement of the condition from the previous problem, so we can use the answer from the previous problem to get this answer.

 

P(doesn't scream and doesn't punch) = 1 - P(screams or punches) = 1 - .74 = .26

 

We could also get this answer from the table: There is one cell in the table corresponding to the condition "doesn't scream and doesn't punch." The number in that cell is 26%, or .26.