20, 40, 60...
15 & 20 have an infinite number of Common Multiples; the first three are 60, 120 and 180.
10, 20 and 30.
4060, 8120, 12180.
20, 40, 60
20, 40, 60
20, 40, and 60.
10, 20, 30
10, 20, 30
140, 280, 420
40, 80 & 120.
140, 280, 420
300, 600, 900