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The number of 5-digit telephone numbers having atleast one of their digits repeated is(A) 90,000 (B) 10,000 (C) 30,240 (D) 69,760 |
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Answer» Answer is (D) Total number of telephone numbers when there is no restriction = 105 Also number of telephone numbers having all digits different = 10P5 Required number of ways = 105 – 10P5 = 1000000 -10x9x8x7x6 = 1000000 - 30240 = 69760 |
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