A student has a collection of 9 CDs, of which 4 are by the Beatles, 3 are by Abba and 2 are by the
Rolling Stones. She selects 4 of the CDs from her collection. Calculate the number of ways in which
she can make her selection if
(i) her selection must contain her favourite Beatles CD, [2]
(ii) her selection must contain 2 CDs by one group and 2 CDs by another.
can some1 explain how to solve this question?