Combination of Atleast One Thing from n Things When All Are Not Different
The number of...
Question
The number of ways in which we can arrange the digits 1, 2, 3....9 such that the product of five digits at any of the five consecutive positions is divisible by 7 is:
A
7!
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B
9P7
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C
8!
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D
5(7!)
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Solution
The correct option is A8! Total number of ways such that any of five consecutive positions is divisible by 7 is such that 7 should be in the middle. ∴ Total number of ways are number of ways of filling the eight left places; i.e. 8!