I'll go for 24 zeros.

Each of the numbers ending in a zero create a zero on the end so that's 9 zero's
the 100 adds 2 more (so total is 11)
BUT 50 adds 2 zeros (2x50) so that is a total of 12 (we already countered one of them)

Each number that ends in 5 also creates zero's (so that's 10 zeros)

BUT 25 and 75 create 2 zeros (2x25 and 6x75) so that's 2 more

Total 24 zeros....



Don't understand why it's 21.......