Question

How many positive five digit integers are there, consisting of the digits 1, 2, 3, 4, 5, 6, 7, 8, 9 in




which one digit appears twice?

Answer 1

there is 1 pair of 5 digit integer
2 and 3 are that digits which appears twice

Answer 2

Answer:

30240

Step-by-step explanation:

Out of 9 select 4.

That is 9C4

Consider the remaining as one.

Now total we have 5 digits

Possible arrangements are 5! / 2! because a digit is repeating

So the answer is

9C4 x (4x5!) / 2! = 30240