单选题
A membership list of 720 people shows that 36 have first and last names that begin with the same letter. If a person is selected at random, what is the probability that his or her first and last name does NOT begin with the same letter?
- (A) 0.05
- (B) 0.25
- (C) 0.50
- (D) 0.75
- (E) 0.95
【正确答案】
E
【答案解析】To solve this problem, first figure out the probability (p) that a person selected at random will have a first and last name that begin with the same letter. Divide the number of people with first and last names that begin with the same letter by the total number of people on the membership list:
[*]
Because all probabilities add up to one, 1-p will equal the number of people whose first and last names do NOT begin with the same letter:
1.00-0.05=0.95