Question

The no of five digit telephone nos having atleast one of their digits repeted​​

Answer 1

Answer:

90

Step-by-step explanation:

number of five digit numbers = 5*4*3*2*1 = 120

number of five digit numbers having one of their digits repeated = 120/2 = 60

number of five digit numbers having two of their digits repeated =120/(2*2)= 30

number of five digit numbers having three of their digits repeated does not exist

so, the answer is 60+30 = 90