The battery life of a fully charged wireless keyboard, in hours, is normally distributed with mean 50 hours and standard deviation 6 hours.
Hannah has a fully charged wireless keyboard.
Find the probability that Hannah's keyboard lasts longer than 45 hours. Give your answer to 3 significant figures.
Hannah has used her keyboard for 45 hours and it is still working. Find the probability that it lasts for at least another 10 hours. Give your answer to 3 significant figures.
390 exam-style questions on OCR A Level Maths 2.4 Statistical Distributions, covering 2.4.1 Discrete probability distributions, 2.4.2 Binomial distribution as a model, 2.4.3 Calculating binomial probabilities, 2.4.4 Mean and variance of the binomial (A-level only), 2.4.5 Normal distribution as a model (A-level only), 2.4.6 Probabilities using the normal distribution (A-level only), 2.4.7 Links to histograms, mean and standard deviation (A-level only), and 2.4.8 Selecting an appropriate distribution (A-level only). Each one has a worked solution and a mark scheme showing where the marks go.