A four digit number is called a doublet if any of its digit is the | Filo
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Class 11

Math

Algebra

Permutations and Combinations

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A four digit number is called a doublet if any of its digit is the same as only one neighbour. For example, is a doublet but is not. Number of such doublets are :

Correct Answer: Option(b)
Solution: Case: 1
Number of ways Ways
Case: 2
Number of ways Ways
Case: 3
Number of ways Ways
Case: 4
Number of ways Ways
Total number of ways
Ways
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