Permutations Practice Test 2

Question : 25 of 30

Marks: +1, -0

The number of 5-digit telephone numbers having at least one of their digits repeated is:

Solution:

A telephone number can be started with zero. Therefore the number of numbers with atleast onedigit repeated

= 10^5 - ^10P_5

= 10^5 – (10 . 9 . 8 . 7 . 6)

= 69760

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