Find the number of different ways of distributing 30 identical objects into 3 identical boxes, so that each box contains at least one object.
NOTE- You cannot distinguish between the objects and the boxes. Also, (10,9,11) and (9,11,10) are one and the same . REMEMBER, the box and the objects are identical!
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Relevant wiki: Identical Objects into Identical Bins
There are a number of identities on the identical objects into identical bins page that can be used for this.
p ( 3 0 , 3 ) = p ( 2 7 , 1 ) + p ( 2 7 , 2 ) + p ( 2 7 , 3 ) = 1 + 1 3 + p ( 2 7 , 3 ) = p ( 2 7 , 3 ) + 1 4
p ( 2 7 , 3 ) = p ( 2 4 , 1 ) + p ( 2 4 , 2 ) + p ( 2 4 , 3 ) = 1 + 1 2 + p ( 2 4 , 3 ) = p ( 2 4 , 3 ) + 1 3
p ( 2 4 , 3 ) = p ( 2 1 , 1 ) + p ( 2 1 , 2 ) + p ( 2 1 , 3 ) = 1 + 1 0 + p ( 2 1 , 3 ) = p ( 2 1 , 3 ) + 1 1
p ( 2 1 , 3 ) = p ( 1 8 , 1 ) + p ( 1 8 , 2 ) + p ( 1 8 , 3 ) = 1 + 9 + p ( 1 8 , 3 ) = p ( 1 8 , 3 ) + 1 0
p ( 1 8 , 3 ) = p ( 1 5 , 1 ) + p ( 1 5 , 2 ) + p ( 1 5 , 3 ) = 1 + 7 + p ( 1 5 , 3 ) = p ( 1 5 , 3 ) + 8
p ( 1 5 , 3 ) = p ( 1 2 , 1 ) + p ( 1 2 , 2 ) + p ( 1 2 , 3 ) = 1 + 6 + p ( 1 2 , 3 ) = p ( 1 2 , 3 ) + 7
p ( 1 2 , 3 ) = p ( 9 , 1 ) + p ( 9 , 2 ) + p ( 9 , 3 ) = 1 + 4 + p ( 9 , 3 ) = p ( 9 , 3 ) + 5
p ( 9 , 3 ) = p ( 6 , 1 ) + p ( 6 , 2 ) + p ( 6 , 3 ) = 1 + 3 + 3 = 7
p ( 1 2 , 3 ) = p ( 9 , 3 ) + 5 = 7 + 5 = 1 2
p ( 1 5 , 3 ) = p ( 1 2 , 3 ) + 7 = 1 2 + 7 = 1 9
p ( 1 8 , 3 ) = p ( 1 5 , 3 ) + 8 = 1 9 + 8 = 2 7
p ( 2 1 , 3 ) = p ( 1 8 , 3 ) + 1 0 = 2 7 + 1 0 = 3 7
p ( 2 4 , 3 ) = p ( 2 1 , 3 ) + 1 1 = 3 7 + 1 1 = 4 8
p ( 2 7 , 3 ) = p ( 2 4 , 3 ) + 1 3 = 4 8 + 1 3 = 6 1
p ( 3 0 , 3 ) = p ( 2 7 , 3 ) + 1 4 = 6 1 + 1 4 = 7 5
Thus, there are 7 5 ways to distribute the 30 objects into the 3 boxes.