How many zeroes are there at the end of the number N, if N = 90! + 180! ?
Choose the correct choice.
A) 15	B) 18	C) 21	D) 24	E) 27

Rationale: "the number of zeroes at the end of 90 ! will be less than the number of zeroes at the end of 180 ! hence it is sufficient to calculate the number of zeroes at the end of 90 ! the number of zeroes = [ 90 / 5 ] + [ 90 / 25 ] + [ 90 / 125 ] = 18 + 3 + 0 = 21 the answer is c ."
Answer: C