UPSC NDA Math Model Paper 5

Digits = 1, 2, 3, …,9
⇒ Total nine digits = 1, 2, 3, …,9
⇒ Total odd numbers = 1, 3, 5, 7, 9 = 5
⇒ ways to form the numbers = 9 × 5
⇒ ways to form the numbers = 45
∴ 45 odd numbers can be composed form the nine digits 1, 2, 3, …,9.