60 and 42 have no common multiples under 100.
21,69
24,48,72,96
15,30,45,60,75,90
100 is the least common multiple of 20 and 25.
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.
Just 90.
28, 56, 84
They are 24, 48, 72, and 96 .
21, 42, 63, 84
Just 77.
36 and 72