Question

How many numbers can be formed from the digits 1, 2, 3, 4 when repetition is not allowed?

Answer 1

Correct Answer - `.^(4)P_(1)+.^(4)P_(2)+.^(4)P_(3)+.^(4)P_(4)`
The number of 1-digit numbers is `.^(4)P_(1)`. The number of 2-digit numbers is `.^(4)P_(2)`. The number of 3-digit numbers is `.^(4)P_(3)`. The number of 4-digit numbers is `.^(4)P_(4)`. Hence, the required number is `.^(4)P_(1)+ .^(4)P_(3)+ .^(4)P_(4)`.