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Arby's 5 for \$5.95

#1 GodSpeed005 Posted 07 May 2007 - 11:38 AM

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8 things to choose from, combinations are made up of 5 things from the original 8. These combinations can do not need to be unique (meaning you can choose 5 of the same thing).

8!/(8-5)! = 8!/3! = 40320/6 = 6720

Is that right?
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#2 sari Posted 07 May 2007 - 12:19 PM

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I'm not exactly sure what the question is, but I do hope this isn't homework you're asking for help on. Although we provide many useful services on this site, and we all have big heads with really large brains, we don't provide homework help.
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#3 GodSpeed005 Posted 07 May 2007 - 02:53 PM

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Homework... lol, I wish I was still in school. No just a "Random Question". Went to Arby's for lunch today and noticed it said "OVER 790 POSSIBLE COMBINATIONS". Was just thinking hmm... how are they figuring that. Me and 3 other tech support guys here were going over and over it and all couldnt agree on the correct math.

Permutation forumla is what I thought, which is what I posted. We couldnt agree on 1 thing, so figured someone here might be a bit more handy in the Discrete Math field.

p.s. Would make a decent homework question now wouldnt it.
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#4 Fenor Posted 07 May 2007 - 02:53 PM

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Yes, 6720 is the correct number of combinations that you can choose when selecting 5 from a list of 8 total items. That means that if you eat at Arby's every day of the year, it will take you 18.4 years before you have a duplicate meal!
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#5 GodSpeed005 Posted 07 May 2007 - 03:00 PM

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AH HAHAHAHA. Thats a gang-load of arby's melts.

More importantly, my math was correct. Now I can say a highschool drop out knows more than college graduates

*LAUGH EVEN MORE!

Edited by GodSpeed005, 07 May 2007 - 03:00 PM.

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#6 sari Posted 07 May 2007 - 03:07 PM

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I told you we had large heads and big brains. Chances are you can find someone here to answer your question, no matter how random it is!
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#7 GodSpeed005 Posted 07 May 2007 - 03:12 PM

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That was a bit random wasnt it.
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#8 sari Posted 07 May 2007 - 03:13 PM

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It was indeed - perhaps you need a hobby?

While you were at Arby's, did you by chance pick me up a mocha milkshake?

Edited by sari, 07 May 2007 - 03:15 PM.

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#9 GodSpeed005 Posted 07 May 2007 - 03:25 PM

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Jamocha? LOL i saw that up there. Our arbys down here in FL. has a new Orange milkshake. Haven't gotten adventurous enough to buy a Orange flavored milkshake. Especially since it's like 100 degrees here and by the time I get back to the office it's half melted.

man my typing skill is going in the toilet.

Edited by GodSpeed005, 07 May 2007 - 03:26 PM.

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#10 sari Posted 07 May 2007 - 03:48 PM

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Jamocha is the best, but they've done a peach one here in the summer that's quite good.
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#11 Kat Posted 07 May 2007 - 05:07 PM

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That orange one is GOOD!
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#12 Lifeandhope Posted 03 June 2007 - 11:17 PM

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I was pondering this very question today and here is what I am wondering. While it is true that you can choose multiples of an item, there are only five spots and some combinations would end up being repeats.

So we are doing 8 Choose 5, but then there are repeats. For instance, four arby's melts and a curly fries is the same as two arbys melts, a curly fries and two more melts.

Help?
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#13 Fenor Posted 05 June 2007 - 08:21 PM

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Combinations was used in the calculation I did above, which allows for repeats. Permutations is where there can be no repeats.
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#14 dsenette Posted 13 June 2007 - 11:45 AM

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#15 Falco98 Posted 20 June 2007 - 09:06 PM

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8 things to choose from, combinations are made up of 5 things from the original 8. These combinations can do not need to be unique (meaning you can choose 5 of the same thing).

8!/(8-5)! = 8!/3! = 40320/6 = 6720

Is that right?

You seem to be thinking of the formula for a combination *without* repitition, but getting it slightly wrong -- the number of combinations you come up with should be much, much lower in that case... your formula should really be 8! / 5!(8-5)! = 40320/720 = 56. But that's the formula for each item only being available for picking once, i.e. you can have 1 melt, 1 drink, 1 fry, etc, whereas the deal really says we could have 5 fries or 5 drinks or whatever.

Thus the problem is that we want combination *with* repitition (i.e. we have 8 things to choose from, and any of them can be repeated all 5 times if we desire).

The proper formula, then, according to wikipedia, is:
(n + r - 1)! / r! (n - 1)!

which works out to 479,001,600 / 604,800.... which, i'm actually kinda surprised, is 792.

At first I'd foolishly believed the answer to be 8 ^ 5, when i sat at arby's... but I didn't think of the fact that that formula counts all permutations, not just combinations, meaning many, many repeats.

So, i'm surprised enough to say, the arby's fliers really are kinda correct. "more than 790 combinations" is rather dead-on.
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