9. Rohit is an engineer who designs roller coasters. He wants to develop a ride that 95% of the population can ride. The average adult in North America has a mass of 73.1 kg with a standard deviation of 14.3 kg. What range of masses should he be prepared to anticipate? [2] 10. A class of 160 students took a nal examination in mathematics. The mean score was 68 and the standard deviation was 13. a) Determine the percentile rank of a score of 38, assuming that the marks were normally distributed. [2] b) What is the probability that someone chosen at random had a mark between 57 and 74? [3]