There are: 10 in between 100 and 200=100,110,120,130.........190, which are multiples of 10.
Therefore, there are: 100 - 10 =90, which are NOT multiples of 10: So that we have:
10 x 100 =100, between 100 and 1,000 which are multiples of 10, and we have:
1,000 - 100=900, between 100 and 1,000 which are NOT multiples of 10.