4-digit numbers are formed with 1, 2, 3 and 4. What is the number of the 4-digit numbers in which at least one digit is repeated?
232
Total 4-digit numbers formed from \(\{1,2,3,4\}\) with repetition allowed \(= 4^{4} = 256\). Numbers with all digits distinct \(= 4! = 24\). So numbers with at least one digit repeated \(= 256 - 24 = 232\).
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