O-LevelMathematicsProbability4024/11 · May/June 2015 · Q255 Marks

A bag contains 5 balls, of which 3 are red and 2 are blue. One ball is taken, at random, from the bag and is not replaced. If this ball is red, another ball is taken, at random, from the bag and is not replaced. This process is repeated until a blue ball is taken from the bag. Part of the tree diagram that represents these outcomes is drawn below. [Figure 25]

(a)Complete the tree diagram.[2]
(b)(i)Expressing each answer as a fraction, find the probability that the second ball taken is blue,[1]
(b)(ii)a blue ball is the second, or the third, ball taken.[2]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (May/June 2015). The mark or mark type is shown in brackets.

[2] Correct third ball branches with 1/3 and 2/3 and correct fourth ball branch(es) with (0 and) 1
B1 for either
[1] 3/10 oe
[2] 1/2 oe
B1 for (3/5) * (2/4) seen

On Oracle Prep you can write or photograph your own answer and have it marked by AI against this mark scheme, with feedback on what you missed.

Topic: Probability, O-Level Mathematics (syllabus 4024). Structured question, 5 marks.
Source: O-Level Mathematics, May/June 2015 Paper 1 Variant 1, question 25.

Questions and mark schemes are from past examination papers and remain the copyright of the exam board. How Oracle Prep builds its content