To find the probability that a number selected from the set {1, 2, 3, ..., 15} is a multiple of 4, we first need to determine how many numbers in the set are multiples of 4.
Multiples of 4 between 1 and 15 are: 4, 8, 12 (There are 3 multiples of 4 in the set)
Total numbers in the set = 15
Therefore, the probability of selecting a number that is a multiple of 4 is:
Probability = Number of favorable outcomes / Total number of outcomes
Probability = 3 (number of multiples of 4) / 15 (total numbers in the set)
Probability = 1/5 = 0.2 or 20%