The battery life, in hours, for a fully charged wireless keyboard is normally distributed with mean 50 hours and standard deviation 6 hours. Hannah has a fully charged wireless keyboard.
Find the probability that the keyboard lasts longer than 45 hours.
Hannah uses her keyboard for 45 hours. Find the probability that Hannah's keyboard lasts for another 10 hours.
Hannah believes that the mean battery life of the wireless keyboards are longer than 50 hours. She took a random sample of 20 of these keyboards and found that their mean lifetime was 51.1 hours. Stating your hypotheses clearly and using a 5% level of significance, test Hannah's belief.
390 exam-style questions on OCR (MEI) A Level Maths 2.4 Probability Distributions, covering 2.4.1 Recognise binomial situations, 2.4.2 Probability of success p, 2.4.3 Calculate binomial probabilities, 2.4.4 Mean of the binomial distribution, 2.4.5 Expected frequencies for binomial, 2.4.6 Probability functions and discrete random variables, 2.4.7 Numerical probabilities for a simple distribution, 2.4.8 Normal distribution as a model (A-level only), 2.4.9 Shape of the Normal curve (A-level only), 2.4.10 Linear transformation and standardising (A-level only), 2.4.11 Symmetry and inflection of Normal curve (A-level only), 2.4.12 Calculate probabilities from a Normal distribution (A-level only), 2.4.13 Model with probability distributions, and 2.4 Probability Distributions. Each one has a worked solution and a mark scheme showing where the marks go.