The annual rainfall in a specific region is normally distributed with a mean of 850 mm. Records show that in 20% of years, the rainfall is more than 1000 mm.
Find the standard deviation of the annual rainfall.
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.