I wasn't sure whether to post this in maths, or in here, so ..... well, it's here now (unless a mod decides to move it ).

Consider the number 100!

How many zeros are there at the end of 100! ????

## How many zeros ????

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### Re: How many zeros ????

... There are two zeros in the number 100. And I suppose an infinate number after a decimal point.

Sexts From The Void wrote:i struggle to maneuver on a chessboard of dicks

### Re: How many zeros ????

horisustar wrote:... There are two zeros in the number 100. And I suppose an infinate number after a decimal point.

I think you missed the !

The question asked "How many zeros are there at the end of 100! ????" (Note the ! - denoting "factorial").

### Re: How many zeros ????

Oh. Meh. Im not really in the mood to think anything maths-y. Sorry. Ill come back and contribute later.

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### Re: How many zeros ????

Numbers which add a 0 to the end:

Anything with 5 as a factor

(There is an abundance of things with 2 as a factor)

so, 5, 10, 15... 100

that's 20.

However, 25, 50, 75 and 100 all have 5 as a factor twice.

So I make it 24 0's.

Anything with 5 as a factor

(There is an abundance of things with 2 as a factor)

so, 5, 10, 15... 100

that's 20.

However, 25, 50, 75 and 100 all have 5 as a factor twice.

So I make it 24 0's.

**Spoiler:**

### Re: How many zeros ????

A good rough estimation is just to divide by four. In fact it's always an overestimation, so a better one is to divide by 4, subtract one, and round up. Here that gives the exact answer. Puzzle: Why does this estimation work?

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### Re: How many zeros ????

Macbi wrote:A good rough estimation is just to divide by four. In fact it's always an overestimation, so a better one is to divide by 4, subtract one, and round up. Here that gives the exact answer. Puzzle: Why does this estimation work?

**Spoiler:**

I'm looking forward to the day when the SNES emulator on my computer works by emulating the elementary particles in an actual, physical box with Nintendo stamped on the side.

"With math, all things are possible." —Rebecca Watson

"With math, all things are possible." —Rebecca Watson

### Re: How many zeros ????

The real answer for any n:

**Spoiler:**

### Re: How many zeros ????

Sorry to post so late, but consider the following:

**Spoiler:**

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