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A four digits number is formed by using only the digits 1,2 and 3 such that both 2and 3 appear at least once. The number of all such four digit number is?
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A four digits number is formed by using only the digits 1,2 and 3 such...
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Formulation of the problem:
To form a four-digit number using only the digits 1, 2, and 3 such that both 2 and 3 appear at least once.

Step 1: Total number of four-digit numbers:
There are 3 options for the first digit (1, 2, or 3) and 3 options for each of the remaining three digits. Therefore, the total number of four-digit numbers that can be formed is 3 x 3 x 3 x 3 = 81.

Step 2: Number of four-digit numbers without 2 or 3:
If 2 and 3 do not appear in the four-digit number, then there are only 1 option for each digit, which is 1. Therefore, the number of four-digit numbers without 2 or 3 is 1 x 1 x 1 x 1 = 1.

Step 3: Number of four-digit numbers with at least one 2 or 3:
To find the number of four-digit numbers with at least one 2 or 3, we subtract the number of four-digit numbers without 2 or 3 from the total number of four-digit numbers:
Number of four-digit numbers with at least one 2 or 3 = Total number of four-digit numbers - Number of four-digit numbers without 2 or 3
= 81 - 1
= 80.
Therefore, there are 80 four-digit numbers that can be formed using only the digits 1, 2, and 3 such that both 2 and 3 appear at least once.
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A four digits number is formed by using only the digits 1,2 and 3 such that both 2and 3 appear at least once. The number of all such four digit number is?
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