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Hi chetan2u, can you please explain your reasoning more? How do you conclude that n! has 3 more zeroes than (n-1)! whenever n! is a multiple of 5!, and further, how do you know that 625 must be eliminated, but not the two multiples of 125 that are greater than 625 but still 3 digit integers? Thoroughly confused on how to start this one. I know that the trailing zeroes depend on the number of 5s in an expression, since the number of 2s is always greater, but I'm not sure how to apply that in this case. A more thorough explanation could help me visualize how to solve this one easier.­

­Consider the examples below:

The number of trailing zeros in 124! is:

124/5 + 124/25 = 24 + 4 = 28.

The number of trailing zeros in 125! is:

125/5 + 125/25 + 125/125 = 25 + 5 + 1= 31.

The number of trailing zeros of 125! is three more than the number of trailing zeros of 124!

However:

The number of trailing zeros in 624! is:

624/5 + 624/25 + 624/125 = 124 + 24 + 4 = 152.

The number of trailing zeros in 625! is:

625/5 + 625/25 + 625/125 + 625/675 = 125 + 25 + 5 + 1 = 156.

The number of trailing zeros of 625! is four more than the number of trailing zeros of 624!

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Bunuel chetan2u can you show how 750 and 875 be part of answer? In those cases difference is 4 not 3
pls correct me if im wrong
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Bunuel chetan2u can you show how 750 and 875 be part of answer? In those cases difference is 4 not 3
pls correct me if im wrong

The number of trailing zeros of 749! is 184:

749/5 + 749/25 + 750/125 + 750/625 = 149 + 29 + 5 + 1 = 184

The number of trailing zeros of 750! is 187:

750/5 + 750/25 + 750/125 + 750/625 = 150 + 30 + 6 + 1 = 187

The difference is 3.

You can check similarly for 875! and 874! to get that the difference there is also 3 (218 and 215 respectively).
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