The factors of 18 are: 1, 2, 3, 6, 9, 18
The factors of 28 are: 1, 2, 4, 7, 14, 28
28 and 90 are both divisible by 2, as they are both even numbers. Additionally, 28 is divisible by 4 and 7, while 90 is divisible by 3, 5, 6, 9, 10, 15, 18, 30, 45, and 90.
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.
138 is not divisible by 18.
18 is not divisible by 5 and 7.
20 is not divisible by 18.
28 and its multiples.
-- Neither 2 nor 5 is divisible by 18. -- 18 is divisible by 2, but not by 5.
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.
The numbers that are divisible by 28 are infinite. The first four are: 28, 56, 84, 112 . . .
All multiples of 18 are divisible by 9. Not all multiples of 9 are divisible by 18.