18N.1.SL.TZ0.T_8

pestleMathematicsAISLPaper 118N· sl-4-6-combined-mutually-exclusive-conditional-independence-prob-diagramssource ↗

A bag contains 5 red and 3 blue discs, all identical except for the colour. First, Priyanka takes a disc at random from the bag and then Jorgé takes a disc at random from the bag.

Complete the tree diagram.

[3]

Find the probability that Jorgé chooses a red disc.

[3]

Markscheme / solution

* This question is from an exam for a previous syllabus, and may contain minor differences in marking or structure.

(A1)(A1)(A1) (C3)

Note: Award (A1) for each correct pair of branches.

[3 marks]

$\frac{5}{8} \times \frac{4}{7} + \frac{3}{8} \times \frac{5}{7}$ (A1)(ft)(M1)

Note: Award (A1)(ft) for their two correct products from their tree diagram. Follow through from part (a), award (M1) for adding their two products. Award (M0) if additional products or terms are added.

= $\frac{5}{8}$ $\left( {\frac{{35}}{{56}},\,\,0.625,\,\,62.5\,{\text{% }}} \right)$ (A1)(ft) (C3)

Note: Follow through from their tree diagram, only if probabilities are [0,1].

[3 marks]

Examiners’ report

[N/A]