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I was given the next question: How many options are there to hand to two people 4 green apples, 3 red apples and 5 yellow apples.

I thought about using the partition method by multiplying each case. Is it the right way of looking at the problem and solving it?

I'm sorry, English isn't my first language and I couldn't find the right definition of partition. What I meant by it, is the number of the options of selecting k items out of n without having any meaning to the order of the selected item and allowing repetition

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    It sounds like you mean [combination](https://en.wikipedia.org/wiki/Combination) rather than [partition](https://en.wikipedia.org/wiki/Partition_(number_theory)). What you need to do is find the number of ways of distributing each type of apple, then multiply the results.2017-01-06
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    @N.F.Taussig Not exactly..combination doesn't allow repetition and in this case it's allowed ( the one I was talking about) :)2017-01-06
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    Are you distributing the entire amount of apples to the two people or are you just giving one apple to each person?2017-01-06
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    Distributing the entire amount2017-01-06
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    @lulu the order doesn't matter plus the apples are identical. Sorry I did not mention it2017-01-06
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    This can be solved using compositions or the "stars and bars" method2017-01-06
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    @Lola That is correct. Each distribution is a [combination with repetition](https://en.wikipedia.org/wiki/Combination#Number_of_combinations_with_repetition).2017-01-06

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At the risk of beating a dead horse, the problem is oversimplified by the fact that there are only $2$ people to spread the fruit around. So it would make more sense to look at it without the constraint of just two people.

But to avoid algebra initially, we can increase the number of people to $3$, and set the fruit basket to $4 \text{ green apples: } \color{green}{\huge \bullet}$; $3 \text{ red apples: } \color{red}{\huge \bullet}$; and $5 \text{ yellow apples: } \color{yellow}{\huge \bullet}$.

Distributing the $4$ (undistinguishable) green apples among three (distinguishable) people (Ann, Paul and Ted) would be equivalent to dividing the apples into three labeled boxes, represented by vertical bars. So for the example where the green apples get divided as...

$$\underset{Ann}{\underbrace{\color{green}{\huge \bullet}}}\quad\quad\underset{Paul}{\underbrace{\color{green}{\huge \bullet}\quad\quad\color{green}{\huge\bullet}}}\quad\quad \underset{Ted}{\underbrace{\color{green}{\huge \bullet}}}$$

the representation is: $$\huge \color{green}{ \bullet}\quad\vert\quad\color{green}{ \bullet}\quad\color{green}{ \bullet}\quad\vert \quad \color{green}{ \bullet}$$

The twist in the procedure is to consider that all the apples may go to one person, for example, to Ted:

$$\huge\vert\quad\vert\quad \color{green}{ \bullet}\quad\quad\color{green}{ \bullet}\quad\quad\color{green}{ \bullet}\quad \quad \color{green}{ \bullet}$$

or split $3$ for Ann, $1$ for Ted, and none for Paul:

$$\huge \color{green}{ \bullet}\quad\quad\color{green}{ \bullet}\quad\quad\color{green}{ \bullet}\quad\vert\quad\vert\quad \quad \color{green}{ \bullet}$$

Hence, for $k=3$ people, we just need $k-1=2$ separators (bars) to split the $4$ green apples. Therefore there are $n =4$ apples and $K-1 =2$ separators arranged as $n + k -1 =6$ "objects" or positions. As soon as the $n=4$ positions occupied by the apples are chosen, the rest of the positions will correspond to the two separators. Or we can choose first the positions occupied by the $k-1$ separators, likewise determining the separation of the apples. Hence the overall number of ways to separate the green apples is:

$$\binom{n+k-1}{n}=\binom{n+k-1}{k-1}=\binom{6}{4}$$

As pointed out before, the same would be done for the red and yellow apples.


For context this post uses the stars and bars method:

For any pair of positive integers $n$ and $k$, the number of $k$-tuples of non-negative integers whose sum is $n$ is equal to the number of multisets of cardinality $k − 1$ taken from a set of size $n + 1.$

Both numbers are given by the multiset number $\displaystyle \left(\!{\tbinom {n+1}{k-1}}\!\right) $, or equivalently by the binomial coefficient $\displaystyle {\tbinom {n+k-1}{k-1}}={\tbinom {n+k-1}{n}}$ or multiset number $\displaystyle {\big (}\!{\tbinom {k}{n}}\!{\big )}.$

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Hint:

How many ways can you distribute only the red apples (ignoring that the other types of apples exist)?

How many ways can you distribute only the green apples (ignoring that the other types of apples exist)?


How many ways can you then distribute the red and green apples?

Additional Hint: The multiplication principle seems helpful here

Continue on then to solve the full problem in a similar fashion

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    So using the combination with repetition method for each of them seperatly and then multiply them with each other is the correct asnwer? I feel as if I need to also divide the result by 3! because the order of distributing does not matter2017-01-06
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    Yes, just multiply, and no dividing by $3!$ is unnecessary. After all, any distribution can be described uniquely by the way in which you distribute the types of apples individually, and regardless of how you distribute a particular color, the number of ways to distribute the remaining colors is unchanged: exactly the requirements necessary to use multiplication principle.2017-01-06
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    Hey JMoravitz, in case I'm asked about n(whereas n is a natural number) people instead of 2 , does the answer change in any way?2017-01-06
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    The general hint I gave still applies, however the technique used to count how many ways you can distribute a single color may become a bit more complicated. With two people you can easily see that it solely depends on how many apples the first person is given so it is easy to calculate (*with $k$ apples, there are $k+1$ different amounts the first person could get*). With more people than that you would use stars-and-bars (*i.e. combination with repitition*) to calculate.2017-01-06
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    So if I'm asked about n people the answer doesn't change except for the number 2?2017-01-06
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    Assuming you are actually using the number $2$ somewhere in the solution specifically in reference to the number of people, yes, that is correct.2017-01-06