A-LevelMathematicsProbability and statisticsMay/June 2017Paper 6 Q611 Marks
(a) The random variable X has a normal distribution with mean μ and standard deviation σ. You are given that σ = 0.25μ and P(X < 6.8) = 0.75. (b) The lengths of metal rods have a normal distribution with mean 16cm and standard deviation 0.2 cm. Rods which are shorter than 15.75 cm or longer than 16.25 cm are not usable. Find the expected number of usable rods in a batch of 1000 rods.
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