What is the HCF of 45 and 90?

HCF of two numbers a & b is b if a is divisible by b.

Here, 90 is divisible by 45 so HCF is 45.

Alternate Methods:

1-

Prime factorization of 45 = 3x3x5

Prime factorization of 90 = 2x3x3x5

From the factorization it is clear that GCF = 3x3x5 = 45

2-

Factors of 45 are 1, 3, 5, 9, 15 & 45.

Factors of 90 are 1, 2, 3, 5, 6, 9, 10, 15, 30, 45 & 90.

Common factors are 1, 3, 5, 9, 15 and 45 and the greatest common factor is 45.