Mathematics for IGCSE & O level - Number (Section 3 - No. 32)

What is the highest common factor (HCF) of 20 and 50?

The factors of 20 are 1, 2, 4, 5, 10, and 20. The factors of 50 are 1, 2, 5, 10, 25, and 50. The HCF is 10.