I've done this one, but the answers in the book are different. Just checking if I'm right.

Q. A box contains 3 red discs and 4 blue discs. Two discs are to be selected together, at random. Find the probability that they will be

a) of the same colour

b) of different colour

Please show all your working clearly, and state the names of the rules you are using (like the and or or rule). Thanks for the help!