Question
Question: The number of 4-digit numbers that can be made with the digits 1, 2, 3, 4 and 5 in which at least tw...
The number of 4-digit numbers that can be made with the digits 1, 2, 3, 4 and 5 in which at least two identical, is
A
45 – 5!
B
505
C
600
D
None of these
Answer
505
Explanation
Solution
The number of numbers when repetition is allowed = 54
The number of numbers when digits cannot be repeated
= 5P5
∴ The required number of numbers = 54 – 5!