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
10, 20, 30
40, 80 & 120.
140, 280, 420
140, 280, 420
10, 20, 30
20, 40, and 60.
20, 40, 60
10, 20, 30.