Thirty per cent of customers subscribe to a premium service. Of the premium subscribers, 80% use the mobile app each week. Of the other customers, 20% use the app each week.
Find the probability that a randomly selected customer uses the app in a given week.
Given that a customer uses the app, find the probability that the customer is a premium subscriber.
Given that a customer does not use the app, find the probability that the customer is not a premium subscriber.
200 exam-style questions on OCR (MEI) A Level Maths 2.3 Probability, covering 2.3.1 Calculate the probability of an event, 2.3.2 Complementary events, 2.3.3 Expected frequency of an event, 2.3.4 Diagrams to calculate probabilities, 2.3.5 Mutually exclusive and independent events, 2.3.6 Add probabilities for mutually exclusive events, 2.3.7 Multiply probabilities for independent events, 2.3.8 Mutually exclusive and independent events (notation) (A-level only), 2.3.9 Venn diagrams for probabilities (A-level only), 2.3.10 Conditional probabilities (A-level only), and 2.3.11 Independence via conditional probability (A-level only). Each one has a worked solution and a mark scheme showing where the marks go.