#1**+5 **

Notice that

n! - (n -1 ) ! =

[n x (n-1) x (n-2) x.......x 3 x 2 x 1 ] - [ (n-1) x (n-2) x.......x 3 x 2 x 1 ]

And factoring out the common term, we have

[ (n-1) x (n-2) x.......x 3 x 2 x 1 ] [n - 1] =

[n-1]! * [n-1]

So....... 1000! - 999! =

999! * (999) ......whatever * that* is !!! (it's huge, to be sure)

CPhill
Oct 22, 2014

#2**+5 **

Chris is of course correct. He just makes it look hard LOL

1000!=999!x1000

so

1000!-999!

= 999!x1000 - 999!x1

I can factor out the 999!

=999!(1000-1)

=999! x 999

Melody
Oct 22, 2014

#3**0 **

It's math....it's * supposed* to look hard......if it looked easy.......the questioners would be on to us!!!!! LOL!!!

CPhill
Oct 22, 2014

#4**+5 **

**What is 1000!-999! Its 99.9% of 1000!**

**= 4.0198487281701667977015873148908e+2567**

heureka
Oct 22, 2014