What is the greatest common factor for 21,24,27

So,

To find the GCF, you have to factor all of the numbers.

21 - - > 3 * 7

24 - - > 2 * 2 * 2 * 3

27 - - > 3 * 3 * 3

Next, you find all the factors that they have in common.

They all have at least one 3, so that means that 3 is the greatest common factor of 21, 24, and 27.