Question
Question: The number of five-digit telephone numbers having at least one of their digits repeated is...
The number of five-digit telephone numbers having at least one of their digits repeated is
A
90000
B
100000
C
30240
D
69760
Answer
69760
Explanation
Solution
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.