Question

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

Answer 1

D. 69,760

Formula:-

Total of of 5-digit telephone numbers = 10⁵

If no number is repeated = ¹⁰P₅

The number of 5-digit telephone numbers having atleast one of their digits repeated is

=10⁵-¹⁰P₅