Permutations and Combinations.

In some questions (like the one given below) we come across a dilemma to either to add or to multiply. Please tell me how do you do these type questions?

Ex--

4 cards are chosen from a pack of 52 cards.In how many of these --

a)Four cards are of same suit

b)two are red cards and two are black cards.

In case (a) we add but in case (b) we multiply.Why?

Thanks

Nitin Gupta , 15 Years ago

Grade 11