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/sci/ - Science & Math

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2444297 No.2444297 [Reply] [Original]

How many ways can we order nine computer programs if program 2 cannot immediately follow
program 1?

>> No.2444302

Order n! now go fuck yourself.

>> No.2444336

9! - 8! = 322560

>> No.2444391

That is correct... how did you know that?

>> No.2444415
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2444415

>>2444391
well i reasoned it out by just presuming 9 was an arbitrary number, so what would have happened if you had said 3?

if the condition is only "how many ways can we order N things" then it is N factorial (=N!) and N can be any number.
but you put in a second condition, so i knew something would be minus'd off.

so yeh, if N = 3, then there are 6 combinations
123 (invalid)
132
213
231
312 (invalid
321
and of these 6 (6 = 3! btw)
2 of them are invalid (because 2 comes after a 1)
and i noticed that 2 is 2!, so my prediction would be that the solution to OP's question would be N! - (N-1)!

so i tested it, what if 4 numbers?
24 combinations, 6 of which were invalid
6 is indeed 3!.
pattern comfirmed.
post [9! - 8!]
??????
PROFIT!

>> No.2445289

>>2444391
9! is the number of ways to order 9 programs; 8! is the number of ways to order 8 programs where program #1 must be immediately followed by #2. Just treat the "block" of #1#2 as one program

>> No.2445302

/sci/
supposing neither 3, nor 2, can come after 1 in sequence.

how many combinations now?

(not homework, just curious as to how to do it, i havent attempted myself yet, i might in a while)

>> No.2445313

>>2444415
Is that you in the picture Ek?

>> No.2445317

>>2445313
no

>> No.2445325

>>2445313
lol silly anon
Everyone knows that EK is a trap

>> No.2445329

>>2445302
<span class="math">9!-8!-8![/spoiler]. Same reasoning as >>2445289, just applied twice.

>> No.2445331

>>2445317
so why the fuck you keep posting pictures of that girl?

>> No.2445338
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2445338

>>2445331
why the fuck do you keep posting pictures of stickmen, if you are not a stick?

>> No.2445341

>>2445331
Plus, i saw a video of that girl a while ago and she sounds exactly like you.
I think you are lying.

>> No.2445344

>>2445289
this is wrong.
"where program #1 must be immediately followed by #2"
they misread the question.
1 and 2 must NOT be in sequence.

>> No.2445348
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2445348

>>2445341
>sounds exactly like you
>sounds like the text you are writing

>> No.2445354

>>2445348
Her ideas were pretty much Ek like.

>> No.2445358

>>2445344
It's correct. There are <span class="math">9![/spoiler] orderings total. There are <span class="math">8![/spoiler] orderings that have #2 immediately following #1. Thus there are <span class="math">9!-8![/spoiler] orderings where #2 does not immediately follow #1.

>> No.2445372

>>2445329
yeh i agree with this.

>> No.2445378

>>2445344
Maybe you misread his reasoning?
It sounds pretty good to me.
Maybe you should think before you post...

>> No.2445383

>>2445378
yeh, i just missed out the last step.
i get it now.

>> No.2445400

>>2445338

why do you pretend to be logical, but make such a fallacious comment like that

>> No.2445403
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2445403

>>2444415
>mfw explaining something purely logical through experimentation

If there are N items, there are N! combinations.
There are N-1 possible locations for the "1 then 2" combination. For each of these, there are (N-2)! combinations for the remaining N-2 items.

N! - (N-1)(N-2)! = N! - (N-1)!

>> No.2445414
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2445414

>>2445400
i was making a point.
reactionface images arn't meant to be me.

pic related, and im not actually boxxy
who knew!?

>> No.2445417
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2445417

>>2445400
you really have to ask?

>> No.2445430

EK is a tripfag AND namefag now, huh? Man, this place has gone down the tubes.

>> No.2445434

>>2445414

reported for posting boxxy on /sci/

>> No.2445451

>>2445430
all tripfags are namefags, they just have tripcodes as well.

>>2445434
posting images of boxxy isnt against the global rules, nor is it against /sci/ specific rules.
your report will be ignored.

>> No.2445462
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2445462

>>2445451

>excessive trolling/flaming
>non board related posts

enjoy you're ban

>> No.2445474

>>2445462
it is neither trolling nor flaming.
and have you seen how many non board related posts there are on this board?
hell, probably nearly as many as are actually science or maths related posts.

...you don't get banned for it.
not unless its some extreme spamming.

>> No.2445478

>>2445474
y r u doin this?

>> No.2445495

>>2445478
doing what?
explaining?

>> No.2445503

By the way, what is the name of that blond girl, EK?

>> No.2445508

>>2445503
Cristina Rad

>> No.2445510

everyone knows EK is just a hippo with horrible brit teeth who has nothing better to do than troll.

just wait for her to be banned