Just 90.
15,18,21,24,27,30,33,36,39,42,45,48,51,54,57,60,63,66,69,72,75,78,81,84,87,90,93,96,99
the common multiples between 1 and 100 for 9 and 10 are just 90!
90 that is all
Common multiples of 9 and 10 are all of the multiples of 90.
Multiples of 9 up to 100 are 9, 18, 27, 36, 45, 54, 63, 72, 81, 90, 99. Multiples of 10 up to 100 are 10, 20, 30, 40, 50, 60, 70, 80. 90, 100. The only common multiple up to 100 of 9 and 10 is 90.
2 and 5 are the prime factors that are common to all multiples of 10.
90
Just 90.
Because 10 is a factor of 100.
Since 10 is a multiple of 5, all multiples of 10 will also be multiples of 5. Test the theory. 30, 50, 100... All multiples of 10, and also of 5.
Just 90.
Just ninety.