What is he highest common factor of 55 and 155?

To find the highest common factor (HCF) of 55 and 155, we first need to list the factors of each number. The factors of 55 are 1, 5, 11, and 55. The factors of 155 are 1, 5, 31, and 155. The highest common factor is the largest number that both lists share, which in this case is 5. Therefore, the highest common factor of 55 and 155 is 5.