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Question
How many number of four digits can be formed with the digits 1, 3, 3, 0?
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Solution
The given digits are 1, 3, 3, 0.
Total numbers that can be formed with these digits =\[\frac{4!}{2!}\]Now, these numbers also include the numbers in which the thousand's place is 0.
But, to form a four digit number, this is not possible.
∴ Numbers in which the thousand's place is fixed as zero = Ways of arranging the remaining digits (1,3 and 3) in three places =\[\frac{3!}{2!}\]
∴ Four digit numbers = Total numbers\[-\] Numbers in which the thousand's place is 0=\[\frac{4!}{2!}\]-\[\frac{3!}{2!}\]= 9
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