How many ways are there to have a collection of $10$ fruits +I am just getting started in my combinatorics class and I came across the following problem in my textbook that I am looking for some help with, thanks!
How many ways are there to have a collection of $10$ fruits from a large pile of identical oranges, apples, peaches, bananas and pears if the collection should include exactly two kinds of fruits?
Since the order is not important here we can systematically list the different combinations to see the different combinations. 
How can I use this equation which I believe is the equation I need
$$C(n,r) = \frac{n!}{(n-r)!r!}$$

First select any two kinds of fruits from the given 5 kinds of fruits.  Number of ways to do so is $\binom {5}{2}$
Now using the star and bars method we have to find the positive integral solutions of the equation 
$$a+b=10$$
Which are simply $\binom {9}{1}$
Hence the answer would simply be $$\binom {5}{2}\binom {9}{1}=90$$
