Question

In combination of n objects taken r a
a time where r is less than or equal to
n, the selection of r objects from
these n objects is​

Answer 1

Answer:

Basically the question says that there is an infinite supply of n distinct objects. We need to select r objects such that each of the n distinct objects is selected at least once. 

Let us first pick 1 object of each type. So, we have n objects. We now need to select r−n objects from the infinite supply provided.

In a way, it is equivalent to distributing r−n objects in n groups where giving 0 to someone is allowed (since we have already assigned 1 to each).

Number of ways of doing this = (n−1)(r−n)+(n)−1C=n−1r−1C=(r−1)−(n−1)r−1C=r−nr−1C

Answer 2

Answer:

sequential arrangment