The number of four-digit numbers that can be made with the digits 1,2,3,4 and 5 in which at least two digits are identical is
A
45−5!
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B
505
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C
600
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D
None of these
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Solution
The correct option is B505 The number of numbers when repetition is allowed is 54. The number of numbers when digits cannot be repeated is 5P5. Therefore, the required number of numbers is =54−5!=505.