EXAMPLE 3.3.8
A jar contains a penny, a nickel, a dime, a quarter, and a half-dollar. Two coins are
randomly selected (without replacement) and their monetary sum is determined.
1. What is the probability that their monetary sum will be 55¢?
A. 1/25
B. 1/32
C. 1/9
D. 1/10
SOLUTION
A monetary sum is determined by which two of the five coins are selected, so the number of different outcomes (the number of different monetary sums) is C(5,2) = 10. There are 10 different outcomes possible. Of these 10 outcomes, exactly one of them is a sum of 55¢, so P(sum is 55¢) = 1/10
2. What is the probability that the monetary sum will be 48¢?
A. 1/10
B. 1/9
C. 1/32
D. 0
SOLUTION
There are 10 possible monetary sums. Of these ten possible outcomes, none of them is a sum of 48¢ (it's not possible to combine two of those coins and have them add up to 48¢), so P(sum is 48¢) = 0/10 = 0.