## Stats: Data and Models (3rd Edition)

$21\%$
By the definition of conditional probability: $P(B|A)=\frac{P(A\cap B)}{P(A)}$. Hence here: $P(\text{fever and sore throat})=P(\text{fever})\cdot P(\text{sore throat|fever})=70\%\cdot30\%=0.7\cdot0.3=0.21=21\%$