Foundation June 2019 Paper 2 Q17

OCRFoundationCurrent spec4 marksTree Diagrams

17 A bag contains 4 red counters and 3 blue counters only.
Jack picks a counter at random and then replaces it.
Jack then picks a second counter at random.

(a) Complete the tree diagram.

Tree diagram. First pick: Red with probability 4/7, Blue with probability blank. Second pick after Red: Red 4/7, Blue blank. Second pick after Blue: Red blank, Blue blank

[2]

(b) Work out the probability that Jack picks two red counters. [2]

Mark scheme (a)

Answer	Marks	Part marks and guidance
\(\dfrac{3}{7}\), \(\dfrac{3}{7}\), \(\dfrac{4}{7}\), \(\dfrac{3}{7}\) correctly placed	2	M1 for 2 or 3 probabilities correctly placed	Accept equivalent fractions, decimals or %’s (3 figures for dec or %)