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# How many ways can 5 identical black balls and 7 identical

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Director
Joined: 29 Oct 2004
Posts: 865
Followers: 2

Kudos [?]: 64 [0], given: 0

How many ways can 5 identical black balls and 7 identical [#permalink]  27 Dec 2004, 13:12
How many ways can 5 identical black balls and 7 identical whie balls be arranged in a row so that no 2 black balls are together?
(A) 56
(B) 64
(C) 65
(D) 316
(E) 560
Intern
Joined: 26 Dec 2004
Posts: 6
Followers: 0

Kudos [?]: 0 [0], given: 0

A : 56
The black balls have to be placed between the 7 white balls.. If we arranage the 7 white balls as _W_W_W_W_W_W_W_. We have 8 spots for balck balls and we have to put 5 of them. therefore required result = 8C5 = 56.
Director
Joined: 29 Oct 2004
Posts: 865
Followers: 2

Kudos [?]: 64 [0], given: 0

Yep (A)
Nice approach.
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