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प्रश्न
In how many ways can 5 children be arranged in a line such that two particular children of them are never together.
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उत्तर
Among the 5! = 120 permutations of 5 children.
There are 48 in which two children are together.
In the remaining 120 – 48 = 72 permutations
Two particular children are never together.
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