{1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25} contains three multiples of 7.
Itself and any other multiples of 7
Five multiples of 42 are 1, 2, 6, 7, 21, 42.
3, 5, 6, 9, 12, etc are all multiples of 3 3, 7, 11, 34 are not multiples of any integer. Notice the first list contains numbers that can all be divided by the same number, 3. Thie second list the numbers cannot be divided by any number except 1.
70, 700, 7000, 70000, 77
28,56.84,112.etc
Multiples of 7 include 7, 14, 21, 28 and so on. For them to be common, they need to be compared to another set of multiples.
Multiples of 6: 12, 18, 24 Multiples of 7: 14, 21, 28
That's an infinite list.
7, 14, 21, 28
Itself and any other multiples of 7
21,42 and 63 are the first three multiples
7, 14, 21
3,6,9,12,15,18,21,24
Five multiples of 42 are 1, 2, 6, 7, 21, 42.
3, 5, 6, 9, 12, etc are all multiples of 3 3, 7, 11, 34 are not multiples of any integer. Notice the first list contains numbers that can all be divided by the same number, 3. Thie second list the numbers cannot be divided by any number except 1.
Example: 5 and 7 List the multiples of 5. 5, 10, 15, 20, 25, 30, 35, 40... List the multiples of 7. 7, 14, 21, 28, 35, 42... The LCM is the first number that appears on both lists.
You can, or you can just multiply them together.