Combination

If the number of selections of r as well as (n + r) things from 5n different things are equal, then what is the value of r?

What is the number of selections of at most 3 things from 6 different things?

What is the number of positive integer solutions of x + y + z = 5?

For the following two (02) items: T

here are 8 points on a plane out of which 4 points are collinear.

How many quadrilaterals can be formed by joining these points?