Question

Ike likes numbers only if the sum of their digits is 9. How many digits between 10-100 does he like? *

Answer 1

There are many divisibility tests. ... 9: A number is divisible by 9 if the sum of its digits is divisible by 9. .... Each number has only two factors: 1 and itself. 6 ...

Answer 2

Ok so its 8 `1&8   2&7 3&6  4&5 and then all of those numbers reversed 
18 27 36 45 and 81  72 63  54