The time taken for a pizza delivery is normally distributed with a mean of 28 minutes. It is found that 15% of deliveries take longer than 35 minutes.
Find the standard deviation of the pizza delivery times.
149 exam-style questions on OCR (MEI) A Level Maths 2.4.12 Calculate probabilities from a Normal distribution (A-level only). Each one has a worked solution and a mark scheme showing where the marks go.