What is the HCF of 20, 45 and 15

5

Step-by-step explanation:

Find the greatest common divisor:

gcd(20, 45, 15)

Find the divisors of each integer and select the largest element they have in common:

The divisors of 20 are:

1, 2, 4, 5, 10, 20

The divisors of 45 are:

1, 3, 5, 9, 15, 45

The divisors of 15 are:

1, 3, 5, 15

The largest number common to all divisor lists is 5:

divisors of 20: 1, 2, 4, 5, 10, 20

divisors of 45: 1, 3, 5, 9, 15, 45

divisors of 15: 1, 3, 5, 15

gcd(20, 45, 15) = 5