20
pinkgal333:20, 40, 60 are all common multiples.
Use some method which you probably already learned, to find the least common multiple. All the other common multiples are multiples of this least common multiple, so you can multiply the least common multiple by 2, by 3, by 4, etc., to get additional common multiples.
Multiples of 2: 2, 4, 6, 8, 10, 12, 14, ... Multiples of 5: 5, 10, 15, 20, 25, 30, ... Multiples of 10: 10, 20, 30, 40, 50, ... So the LCM (Least Common Multiple) is 10.
20
60 and its multiples
The Least Common Multiple (LCM) for 2 4 is 4.