(i)     Write down the value of $q$.

(ii)     Find the value of $p$.

Find ${\text{P}}(B)$.

(i)     $q = 0.1$     A1     N1

(ii)     appropriate approach     (M1)

eg$\,\,\,\,\,$${\text{P}}(A) - q,{\text{ }}0.4 - 0.1$

$p = 0.3$    A1     N2

[3 marks]

valid approach     (M1)

eg $\,\,\,\,\,$${\text{P}}(A \cup B) = {\text{P}}(A) + {\text{P}}(B) - {\text{P}}(A \cap B),{\text{ P}}(A \cap B) + {\text{P}}(B \cap A')$

correct values     (A1)

eg$\,\,\,\,\,$$0.8 = 0.4 + {\text{P}}(B) - 0.1,{\text{ }}0.1 + 0.4$

${\text{P}}(B) = 0.5$    A1     N2

[3 marks]

This question was well done by most candidates. In part (b), the intersection ${\text{P}}(A \cap B)$ was sometimes overlooked, incorrectly using ${\text{P}}(A \cup B) = {\text{P}}(A) + {\text{P}}(B)$ instead.

This question was well done by most candidates. In part (b), the intersection ${\text{P}}(A \cap B)$ was sometimes overlooked, incorrectly using ${\text{P}}(A \cup B) = {\text{P}}(A) + {\text{P}}(B)$ instead.