What is the highest common factor of 10 and 25?

The highest common factor (HCF) of 10 and 25 is 5. This is because 5 is the largest positive integer that divides both 10 and 25 without leaving a remainder. The factors of 10 are 1, 2, 5, and 10, while the factors of 25 are 1, 5, 25. The highest common factor is the greatest number that appears in both lists, which in this case is 5.