What is the answer to this?

How many zeros are there at the end of 25!?

What number combination makes up a 0 in the units place? (prime factor): 2 and 5 because 5 x 2 = 10 which has a ‘0’. to find number of zeroes, just find how many 5’s you have in all, since number of 5’s will be less than number of 2’s (limiting factor / bottleneck). so we got 5’s in 5,10,15,20,25. total = 5.

but the problem does not end here because 25 = 5 x 5. We got an extra 5! so total 5’s are 6. That would be the answer.