Statistics

8. A Mathematics 30 examination was written by 1350 students and the results were normally distributed. What is the number of students who achieved a mark within 1.37 standard deviations of the mean? Clearly document your calculator entries, using the calculator statistics functions. (2 marks) 9. A manufacturer that guarantees its car tires for 80 000 km find 2.5% of its tires are returned under the warranty. Assuming a normal distribution and a standard deviation of 1250 km, what is the mean life of the tires, correct to the nearest kilometre? Clearly document your calculator entries, using the calculator statistics functions. (2 marks) 10. A company produces Frisbees. The Frisbees have a mean mass of 172.0 g, with a standard deviation of 0.8 g. To ensure that few Frisbees are rejected, the manager must make sure that the mean mass of the Frisbees lies in the acceptable range of 171.7 g to 172.2 g. What is the margin of error used for their quality control tests? (1 mark)