Number 2, 4, 6, 8, 10.....196, 198, 200 are multiplied together. The number of zeros at the end of the product on the right will be equal to -

$$\eqalign{ & {\text{2, 4, 6, 8, 10}}......{\text{198, 200 }} \cr & {2^{100}}(1 \times 2 \times 3 \times ..... \times 99 \times 100) \cr} $$
$$\eqalign{ & \underline {5\,\,\,|\,\,100} \cr & \underline {5\,\,\,|\,\,\,20} \,\,\,\,\, = 24{\text{ zero's (20 + 4)}} \cr & \,\,\,\,\,|\,\,\,4 \cr} $$
When we multiply the series of 1 × 2 × 3 ×..... × 100 then we find 24 zero at the end of the product