A call centre claims that the amount of time a worker spends on each phone call can be modelled by a normal distribution with a mean of 8 minutes and a standard deviation of 2 minutes.
Show that the standardised value for 11 minutes is 1.5.
Hence, using this model, find the probability that the time the worker spends on a randomly selected phone call is more than 11 minutes.
The call centre manager thinks that the mean time for each phone call is more than 8 minutes. The manager takes a random sample of 20 phone calls and finds that the average time is 8.8 minutes. Test the manager's belief at the 5% significance level. You should state your hypotheses clearly.
616 exam-style questions on Edexcel A Level Maths The Normal Distribution, covering 3.1 The Normal Distribution, 3.2 Finding Probabilities for Normal Distributions, 3.3 The Inverse Normal Distribution Function, 3.4 The Standard Normal Distribution, 3.5 Finding the mean and standard deviation, 3.6 Approximating a Binomial Distribution, and 3.7 Hypothesis Testing with the Normal Distribution. Each one has a worked solution and a mark scheme showing where the marks go.