15 & 20 have an infinite number of Common Multiples; the first three are 60, 120 and 180.
10, 20, 30 The common multiples of 5 and 10 are multiples of their lowest common multiple. The lcm of 5 and 10, is 10. Thus the first three common multiples are 10, 20, 30.
1, 660, 5580
40, 80 & 120.
10, 20, 30.
They are: 180, 360 and 540
100, 200, 300
20, 40 and 60
20, 40, 60.
10, 20, 30.
20 30 40
140, 280, 420