Sir, we can get zero by two cases.

I. When we multiply 2 by 5 and

II. When already there is zero at the end.(like in 10)

So taking forward your solution, we get 21 zero's from I case and two more zero's from II case i.e. from 10 and 20.

Final answer would be =21+2=23.

I. When we multiply 2 by 5 and

II. When already there is zero at the end.(like in 10)

So taking forward your solution, we get 21 zero's from I case and two more zero's from II case i.e. from 10 and 20.

Final answer would be =21+2=23.