CAT (QA) PYQs

How many numbers with two or more digits can be formed with the digits $1,2,3,4,5,6,7,8,9,$ so that in every such number, each digit is used at most once and the digits appear in the ascending order?

How many integers in the set $(100,101,102, \ldots, 999)$ have at least one digit repeated?

The number of groups of three or more distinct numbers that can be chosen from 1,2, $3,4,5,6,7$ and $8$ so that the groups always include $3$ and $5$, while $7$ and $8$ are never included together is