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?

In how many ways can $7$ identical erasers be distributed among $4$ kids in such a way that each kid gets at least one eraser but nobody gets more than $3$ erasers?

The number of ways of distributing $20$ identical balloons among $4$ children such that each child gets some balloons but no child gets an odd number of balloons, is