newbie49
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January 17th, 2011 at 8:50:29 AM permalink
One of wizard's site, mathproblems.info, it has this Chicken McNugget problem:

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At McDonalds you can order Chicken McNuggets in boxes of 6, 9, and 20. What is the largest number such that you can not order any combination of the above to achieve exactly the number you want?
---

The answer wizard gave is 43. Does the wizard mean smallest number? not the largest?
I thought the largest will be any big prime number, meaning the answer is infinite...
dwheatley
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January 17th, 2011 at 9:00:54 AM permalink
No, Wizard is right. You can make all sorts of prime numbers by ADDING up chicken mcnugget boxes. 20 + 9 = 29, which is prime. 9*3 +3*20 = 97 which is prime. And so forth.

EDIT: since 93 isn't prime... I will pick 97 as my next example, which I'm pretty sure is.

His solution pretty rigourously explains how you can be absolutely sure there are no numbers hiding above 43 that can't be made.
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Toes14
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January 17th, 2011 at 11:06:04 AM permalink
One problem with this is that McDonald's now has 10 piece boxes instead of 9 piece boxes, so the parameters have changed.
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boymimbo
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January 17th, 2011 at 11:57:33 AM permalink
93 is prime? (31 x 3)
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DJTeddyBear
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January 17th, 2011 at 12:01:56 PM permalink
Quote: Toes14

One problem with this is that McDonald's now has 10 piece boxes instead of 9 piece boxes, so the parameters have changed.

Not only that, many McDonalds now have a 4 piece on the Dollar Menu!
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AZDuffman
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January 17th, 2011 at 12:10:12 PM permalink
The bigger question is why would anyone want to eat so many Chicken McNuggets?
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newbie49
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January 17th, 2011 at 12:21:29 PM permalink
ah...my bad
mkl654321
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January 17th, 2011 at 12:44:23 PM permalink
No, no, the answer is easy. You buy two 20s, and one 6. Then you open up the box of 6 and feed three of them to the dog. Voila! You have 43.
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Toes14
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January 17th, 2011 at 2:16:47 PM permalink
Quote: mkl654321

No, no, the answer is easy. You buy two 20s, and one 6. Then you open up the box of 6 and feed three of them to the dog. Voila! You have 43.



I think the key word is ORDER. In your example, you ordered 46 McNuggets, not 43.
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mkl654321
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January 17th, 2011 at 7:26:07 PM permalink
Quote: Toes14

I think the key word is ORDER. In your example, you ordered 46 McNuggets, not 43.



Okay, you bribe the cook to put an extra 3 nuggets in one of your two boxes of 20.
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Wizard
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January 17th, 2011 at 9:01:43 PM permalink
The question is what is the largest number that you CAN'T order from boxes of 6, 9, and 20.

I've had people challenge me from time to time, throwing huge primes at me. However, it is easy to fill most of the order with 20-piece boxes, and use 6-piece and 9-piece boxes to get to the target exactly. Give me any number bigger than 43 and I'll show you an answer.

On a more practical note, a friend of mine once made a bet that he could eat 100 McNuggets. I think he got to 86 when he admitted defeat.
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EvenBob
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January 17th, 2011 at 9:05:29 PM permalink
Quote: Wizard

a friend of mine once made a bet that he could eat 100 McNuggets. .



Good god. The damn things are dry and tasteless, they taste like whatever you dip them in. Yuk.
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Wizard
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January 17th, 2011 at 9:20:23 PM permalink
Quote: EvenBob

Good god. The damn things are dry and tasteless, they taste like whatever you dip them in. Yuk.



I could say the same thing, but must admit, I loved McDonalds as a kid. Who didn't? Even in college, I don't think I could get to 100, but would have enjoyed the challenge. In my prime I think I could have easily made 60.
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mkl654321
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January 17th, 2011 at 9:22:54 PM permalink
Quote: Wizard

The question is what is the largest number that you CAN'T order from boxes of 6, 9, and 20.

I've had people challenge me from time to time, throwing huge primes at me. However, it is easy to fill most of the order with 20-piece boxes, and use 6-piece and 9-piece boxes to get to the target exactly. Give me any number bigger than 43 and I'll show you an answer.

On a more practical note, a friend of mine once made a bet that he could eat 100 McNuggets. I think he got to 86 when he admitted defeat.



So what is it about the relationships of those numbers and the number 43? The LCM of 6, 9, and 20 is 180, which for some reason makes me think that has something to do with the answer, but I'm at a loss to say why.
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EvenBob
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January 17th, 2011 at 9:24:48 PM permalink
Quote: Wizard

I could say the same thing, but must admit, I loved McDonalds as a kid.



I loved Mc's as a teen because I could get 4 burgers and 4 fries for $1.25, which lasted to about 1968 when they raised it to 20 cents each.
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Wizard
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January 17th, 2011 at 9:59:26 PM permalink
Quote: mkl654321

So what is it about the relationships of those numbers and the number 43? The LCM of 6, 9, and 20 is 180, which for some reason makes me think that has something to do with the answer, but I'm at a loss to say why.



I think you're overthinking it. Here is my solution.
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dwheatley
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January 18th, 2011 at 4:51:14 AM permalink
6 chicken mcnuggets weigh 114g (source). 310 calories, 21g of fat, and 670 mg of sodium.

Multiply by 100/6, to get:

1900g, 5167 calories, 350g of fat, 11167mg of sodium.

4.2 lbs, double the average daily calorie intake, over 5 times your recommended daily fat intake, and over 4.5 times your recommended sodium intake.

Gross.
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DJTeddyBear
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January 18th, 2011 at 4:58:32 AM permalink
Quote: mkl654321

So what is it about the relationships of those numbers and the number 43? The LCM of 6, 9, and 20 is 180, which for some reason makes me think that has something to do with the answer, but I'm at a loss to say why.

The significance is that you have both even and odd package sizes. Therefore, there is a maximum number of nuggets, 43, that you can't achieve when you combine those package sizes.

As was already mentioned, McDonalds now has a 4 piece box, and in some locations have dropped the 9 piece box. (Some have replaced it with a 10 piece box.)

That being the case, it's easy to see that with a 4, 6, and 20 piece choices, you can combine to make any even number of nuggets except 2. It's irrelevant that the LCM is 60.
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Wizard
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January 19th, 2011 at 3:37:35 PM permalink
The posts about the challenge to eat 100 Chicken McNuggets has been moved to Chicken McNugget Eating Challenge.
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Wizard
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January 19th, 2011 at 3:39:52 PM permalink
I'm still trying to find an algebraic solution for a general case of x, y, and z packs.

Here is what I have so far. If x and y are both prime, then the largest number of McNuggets you can't exactly buy is xy - x - y.
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Wizard
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January 19th, 2011 at 7:25:50 PM permalink
Sorry to keep talking to myself in this thread, but according to Wikipedia there is no known solution for the case of 3 or more box sizes of McNuggets.
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Nareed
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January 19th, 2011 at 7:29:28 PM permalink
Quote: Wizard

Sorry to keep talking to myself in this thread, but according to Wikipedia there is no known solution for the case of 3 or more box sizes of McNuggets.



You should find the solution, then anounce it but never publish it: The Wizard's Last Theorem.
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algle
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January 19th, 2011 at 7:32:35 PM permalink
Quote: Wizard

Sorry to keep talking to myself in this thread, but according to Wikipedia there is no known solution for the case of 3 or more box sizes of McNuggets.



That's probably a good thing. No-one buying McNuggets should be faced with more than 3 choices of box size.
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