Find no. of zeros at the end of the product of multiple numbers

Q : Find the number of zeros at the end of the product
a. Of first 100 multiples of 10
b. 5X10X15X20X25X30X35X40X40X45
C. 100!

I would also like to know whether this kind of question is possible in GMAT and what would be the complexity level.

OA-
1. 124
2. 10
3. 24