5 digit telephone numbers having at least one of their digits repeated is
= total possible 5 digit telephone numbers - 5 digit telephone numbers without any digit being repeated.
=(10*10*10*10*10)-(10*9*8*7*6)
=100000-30240
=69760
763920
6561
500
7
987,653
763920
98,764
It is possible to create a 3-digit number, without repeated digits so the probability is 1.
6561
There are 5*4*3 = 60 such numbers.
757
With repeated digits, 43 = 64 Without repeated digits, 4*3*2 = 24
24
500
7
9x9x8x7x6x5x4x3 =1632960
987,653