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Question

The number of five-digit telephone numbers having at least one of their digits repeated is

  1. 90000
  2. 100000
  3. 30240
  4. 69760

The correct answer is: 69760


    The number of five-digit telephone numbers which can be formed using the digits 0, 1, 2 ….9 is 105 . The number of five-digit telephone number which have none of their digits repeated is 10P5 = 30240. Thus, the required number of telephone number is 105 – 30240 = 69760.

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