The number of 4-digit numbers that can be made with the digits 1, 2, 3, 4, 5 in which at least two digits are identical is 

  • Option 1)

    45 - 5!

  • Option 2)

    505

  • Option 3)

    600

  • Option 4)

    None of these

 

Answers (1)

As learnt in concept

Factorial Notation -

The product of first n natural numbers. n! = n(n - 1) (n - 2) ..........3 . 2 . 1

- wherein

Where n\epsilon N

 

 digits are 1, 2, 3, 4, 5

Total number of 4 digits numbers = 5 X 5 X 5 X 5

Numbers with no identical digits =5!=120

Thus, required number =625-120=505


Option 1)

45 - 5!

This is incorrect option

Option 2)

505

This is correct option

Option 3)

600

This is incorrect option

Option 4)

None of these

This is incorrect option

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