Answer:
1, 3, 5
Step-by-step explanation:
1 is a common factor because all numbers are divisible by 1
3 is a common factor because all the numbers are divisible by 3 (or in other words multiples of 3)
5 is a common factor of all those numbers because the last digit place in 15, 45 and 90 end in 5 and/or 0
If you're looking at 90 individually, then the common factors are 1, 2, 3, 5, 6, 9, 10, 15, 30, 45, 90
If you're looking at 45 individually, then the common factors are 1, 3, 5, 9, 15, 45
If you're looking at 15 individually, then the common factors are 1, 3, 5, 15
