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  • The number of 5-digit telephone numbers having at least one of their digits repeated is A. 90,000

The number of 5-digit telephone numbers having at least one of their digits repeated is
A. 90,000
B. 10,000
C. 30,240
D. 69,760

Answers (1)

The answer is the option (d).

Total number of telephone numbers when there is no restriction =  10^5

Number of telephone numbers with all digits different = ^{10}P_5

Required number of ways=10^5-^{10}P_5 =100000-10*9*8*7*6

=100000-30240=69760

Posted by

infoexpert21

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