Question

There is a spinner with 15 equal areas, numbered 1 through 15. If the spinner is spun one time, what is the probability that the result is a multiple of 3 or a multiple of 4?

Answer 1

Multiples of 3 from 1 to 15: 3, 6, 9, 12, 15 (5 numbers).
Multiples of 4: 4, 8, 12 (3 numbers).
Overlap (multiples of 12): 12 (1 number).

By inclusion-exclusion: 5 + 3 − 1 = 7 favorable outcomes. Probability = 7/15.