think of multiples as multiplication tables
multiples of 3 are :
3 x 1 = 3
3 x 2 = 6
3 x 3 = 9
so multiples of 3 are (3,6,9,12,15,18)
same as multiples of 100...
100 x 1 = 100
100 x 2 = 200
100 x 3 = 300
so multiples of 100 are (100,200,300)
the common multiple of 3 and 100 is 300
