13 A bag contains 4 black discs and 5 white discs.
Ranjit takes a disc at random from the bag and notes its colour. He then replaces the disc in the bag. Ranjit takes another disc at random from the bag and notes its colour.
(a) Complete the probability tree diagram to show all the possibilities.(4)
(b) Calculate the probability that Ranjit takes two discs of different colours. (3)
Mark scheme (a)
Scheme
Marks
\(\frac{4}{9}\) or \(\frac{5}{9}\) seen
B1
Correct structure
B1
\(\frac{4}{9}\) or \(\frac{5}{9}\) correctly placed once
