Just a normal arrangement problem!

5 5 balls of different colours are to be placed in 3 3 boxes of different sizes. Each box can hold all 5 5 balls. Then in how many different ways can we place the balls so that none of the box remains empty? If the answer is N \text{N} , find the value of N 30 + 4 ! \dfrac{\text{N}}{30} + 4!


The answer is 29.

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3 solutions

Kunal Joshi
Jun 3, 2014

Since, none of the box can't be kept empty, there are only two possibilties in which we can distribute the balls in 3 boxes. It is (3,1,1) or (2,2,1). And as the boxes and balls are of different size and colour respectively, we can arrange them among themselves in 3 ways. So total number of ways is, ( ( 5 3 ) ( 3 1 ) ( 1 1 ) + ( 5 2 ) ( 3 2 ) ( 1 1 ) ) 3 ( \dbinom{5}{3} \dbinom{3}{1} \dbinom{1}{1} + \dbinom{5}{2} \dbinom{3}{2} \dbinom{1}{1} ) 3 = 150 = \boxed{150} Hence, N = 150 so answer is, 150 30 + 4 ! = 29 \dfrac{150}{30} + 4! = \boxed{29}

I disagree with multiplying by 3 ! 3! , because there are only 3 distinct ways to arrange (3, 1, 1). The only choice is for which box to contain 3 balls, and there is only 1 way to do this.

hence, the answer should be 150 30 + 4 ! = 29 \frac{ 150}{30} + 4! = 29 .

Calvin Lin Staff - 7 years ago

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No, all the boxes are of different size then how can you say that there is only 3 ways to arrange them? Each time you keep 3 balls in a box, there are 2 possibilities for other two. So total is 3 x 2 i.e. 3!

Kunal Joshi - 7 years ago

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Let's call the boxes Red, Blue and Green. We can choose to either have 3 balls in Red, 1 each in Blue and Green, or we can choose to have 3 balls in Blue, 1 each in Green and Red, or we can choose to have 3 balls in Green, 1 each in Red and Blue. This gives us 3 ways. If you say that there are 6 ways, please state the other 3.

The objections to your argument pointed out that the maximium possible number of permutations (without any restictions) is 3 5 = 243 3^5 = 243 . How can there be 300 > 243 300 > 243 such ordering?

Calvin Lin Staff - 7 years ago

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@Calvin Lin Oh yes! Now I got what mistake I was doing. Sorry for inconvinience caused to you!

Kunal Joshi - 7 years ago

Typo: ( 5 3 ) ( 2 1 ) ( 1 1 ) \large\binom{5}{3}\large\binom{*2*}{1}\large\binom{1}{1}

btw nice solution. ^__^

Samuraiwarm Tsunayoshi - 6 years, 11 months ago

Aargh! I got tricked! I put down 150 and then gave up! -_-

Gavin LO - 6 years ago
Venture Hi
Oct 26, 2014

Use the Stirling numbers of the second kind sequence where S(k,n) n! where k is number of balls and n number of boxes. In this case, S(5,3)=25 3!=150 ways. Since the answer is N/30 + 4!, answer is 29

Let's give boxes a name, A B and C.

First case: (3,1,1)

  • Choose 3 balls from 5 balls for box A, ( 5 3 ) \large\binom{5}{3} .
  • Choose 1 ball from 2 balls for box B, ( 2 1 ) \large\binom{2}{1}
  • Choose 1 ball from 1 ball for box C, ( 1 1 ) \large\binom{1}{1}
  • You can choose box A or B or C to have 3 balls and the other have 1 ball, ( 3 2 ) \large\binom{3}{2}

This case will have ( 5 3 ) ( 2 1 ) ( 1 1 ) ( 3 2 ) = 60 \large\binom{5}{3}\large\binom{2}{1}\large\binom{1}{1}\large\binom{3}{2} = 60 ways.

Second case: (2,2,1)

  • Choose 2 balls from 5 balls for box A, ( 5 2 ) \large\binom{5}{2} .
  • Choose 2 balls from 3 balls for box B, ( 3 2 ) \large\binom{3}{2}
  • Choose 1 ball from 1 ball for box C, ( 1 1 ) \large\binom{1}{1}
  • You can choose box A or B or C to have 1 ball and the other have 2 balls, ( 3 2 ) \large\binom{3}{2}

This case will have ( 5 2 ) ( 3 2 ) ( 1 1 ) ( 3 2 ) = 90 \large\binom{5}{2}\large\binom{3}{2}\large\binom{1}{1}\large\binom{3}{2} = 90 ways.

Therefore, there're total of 60 + 90 = 150 60+90 = 150 ways to do that.

Answer: 29 \boxed{29} . :3

wow! you solution is great.

Shohag Hossen - 5 years, 11 months ago

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