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

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

valid interpretation (may be seen on a Venn diagram)     (M1)

eg$\,\,\,\,\,$${\text{P}}(A \cap B) + {\text{P}}(A' \cap B),{\text{ }}0.2 + 0.6$

${\text{P}}(B) = 0.8$     A1     N2

[2 marks]

valid attempt to find ${\text{P}}(A)$     (M1)

eg$\,\,\,\,\,$${\text{P}}(A \cap B) = {\text{P}}(A) \times {\text{P}}(B),{\text{ }}0.8 \times A = 0.2$

correct working for ${\text{P}}(A)$     (A1)

eg$\,\,\,\,\,$$0.25,{\text{ }}\frac{{0.2}}{{0.8}}$

correct working for ${\text{P}}(A \cup B)$     (A1)

eg$\,\,\,\,\,$$0.25 + 0.8 - 0.2,{\text{ }}0.6 + 0.2 + 0.05$

${\text{P}}(A \cup B) = 0.85$     A1     N3

[4 marks]