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  4. Number of 5 digit numbers that can be made using the digits 1 and 2 and in which at least one digit is different.

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Q. Number of $5$ digit numbers that can be made using the digits $1$ and $2$ and in which at least one digit is different.

Permutations and Combinations

Solution:

Total number of numbers without restriction $=2^{5}$
Two numbers have all the digits equal. So,
The required number $=2^{5}-2=30$