How many zeros does 90! end with?
The number of zeros at the end of n! is determined by the number of 5’s. To find this you do the following process: n/5 = n1 and some remainder.
Drop the remainder and compute n1/5 = n2 plus some remainder.
Drop the remainder and compute n2/5 = n3 plus some remainder, etc.
The number of zeros is n1+n2+n3+n4...
90/5=18
18/5=3
so thenumber of zeros =20=3 = 23