How do you determine the GFC and the LCM of 25 and 90?

Answer 1

Factor them.
5 x 5 = 25
2 x 3 x 3 x 5 = 90
Select the common factor.
The GCF is 5.
Combine the factors, eliminating duplicates.
2 x 3 x 3 x 5 x 5 = 450, the LCM
Check it.
25 x 90 = 2250
450 x 5 = 2250
It checks.