What is the HCF of 42 49 and 84?

The Highest Common Factor (HCF) of 42, 49, and 84 is 7. To find the HCF, you need to factorize each number into its prime factors. The prime factors of 42 are 2 x 3 x 7, the prime factors of 49 are 7 x 7, and the prime factors of 84 are 2 x 2 x 3 x 7. The HCF is the product of the common prime factors raised to the lowest power they appear in any of the numbers, which in this case is 7.