JEE Advanced Mathematics question
The number of ways in which 9 flowers, of which 5 are identical and white, and the other four are of different colours, can be set on a garland so that no two of the coloured flowers are consecutive, is
Answer: (D)
Solution
Put the 5 identical white flowers in a ring first. Because they are identical, this can be done in only 1 way, and it leaves 5 gaps, one between each pair of neighbouring whites.
No two coloured flowers may be adjacent, so each gap holds at most one coloured flower. We fill 4 of the 5 gaps. The 5 gaps are all alike
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