Answer:
45% that either would occur, or a 5% chance both would occur.
Step-by-step explanation:
There is one overlap, 15, so it must be subtracted from one of the number lists.
3 6 9 12 15 18
5 10 15 20
6/20 + 3/20 = 9/20 = 0.45 = 45%
15 is the ONLY overlap number, so 1/20 times both would occur.
1/20 = 0.05 = 5%
