How many numbers can be formed from the digits 1, 3, 5, 9 if repetition of digits is not allowed?
To find: number of numbers that can be formed from the digits 1, 3, 5, 9 if repetition of digits is not allowed
Forming a 4 digit number:4!
Forming a 3 digit number:4C3 × 3!
Forming a 2 digit number:4C2 × 2!
Forming a 1 digit number:4
So total number of ways=4! + ( 4C3 × 3!) + ( 4C2 × 2!) + 4
=24 + 24 + 12 + 4
=64