The factors of 18 are: 1, 2, 3, 6, 9, 18
The factors of 28 are: 1, 2, 4, 7, 14, 28
They are divisible by 1 and 2.
28 is not divisible by 3.
28 is divisible by 1, 2, 4, 7, 14, 28.
28 is divisible by: 1, 2, 4, 7, 14, 28.
20 is not divisible by 18.
18 is not divisible by 5 and 7.
138 is not divisible by 18.
19. All even numbers except 2 are divisible by 2 and so not prime - that eliminates 16, 18, 20, 28, 36 to leave 19. 33. 33 is divisible by 3 since 3+3 = 6 which is divisible by 3, leaving just 19 which is prime.
28 and its multiples.
-- Neither 2 nor 5 is divisible by 18. -- 18 is divisible by 2, but not by 5.
The numbers that are divisible by 28 are infinite. The first four are: 28, 56, 84, 112 . . .
28, 56, 84, and all other multiples of 28 that are factors of other numbers are also divisible by 28.
All multiples of 18 are divisible by 9. Not all multiples of 9 are divisible by 18.