One way working this out is to find all the numbers that go into 90 by listing all the pairs of numbers that multiply to give 90
1 × 90
2 × 45
3 × 30
6 × 15
9 × 10
From here we can do trial and error:
Let's choose any two factors, say 2 and 3
By listing their multiples, we will find their LCM is 6, not 90
Then choose any two factors, say 3 and 6
By listing their multiples, we will find their LCM is 6, not 90
We can try some bigger number, say 45 and 90
by listing their multiples, we will find their LCM 90
Answer: 45 and 90