10 ll 12 13 14 15 16 17 18 19 20 Original class interval frequencies can be obtained by multiplying the respective relative frequencies by the total number of observations The following data, reported by a sample of students, are the number of movies seen in a movie theatre during past six months. 6 6 9 12 6 4 8 15 E5 The frequency of students who saw 6 movies is 6. The arithmetic mean is the sum of the data values divided by the number of observations. P[A n B) is PiBlAinta) P [A n B :I =0 means that A and B are mutually exclusive events. Mutually exclusive events imply that if one event occurs, the other cannot occur. An event (e.g., A ) and its complement are always mutually exclusive. P IIAfI+P II A): 1 When events are not mutually exclusive, the rule is: P [A U BEZP II AHP [B :l P [ A n B) Rule of addition when event are mutually exclusives: P [A U B :l: P I: A] +P | B :I PI'B n A) is not PI'A|Bj|*P(B} The P(x) is always 0 5 P(x) 5 1. Events are independent when the occurrence of one event has no effect on the probability that another will occur