The operational endurance of a random sample of 15 'Volt-X' industrial sensors is measured under standard load. The mean endurance of the sample is recorded as 118.4 hours118.4\text{ hours}118.4 hours. The endurance times of these sensors are known to follow a normal distribution.
Given that the population standard deviation for these sensors is 4.2 hours4.2\text{ hours}4.2 hours,
estimate the limits between which 95%95\%95% of the endurance times of individual sensors lie.
find a 98%98\%98% confidence interval for the mean endurance time of the 'Volt-X' sensors.
A quality control engineer claims that the true mean endurance time of these sensors is 121.5 hours121.5\text{ hours}121.5 hours.
Comment on the engineer's claim. Give a reason for your answer.
132 exam-style questions on Edexcel A Level Maths 3.7 Hypothesis Testing with the Normal Distribution. Each one has a worked solution and a mark scheme showing where the marks go.