b) EBS's main fleet of buses was bought from Sumo Motors eight years ago. There are feedbacks from passengers and residents living along the bus routes that the buses are noisy, especially when starting from rest at bus stops and traffic lights. This prompted EBS to use simple random sampling to collect a sample of data on Sumo buses' starting-noise levels during the bus operations. EBS is planning to purchase the next fleet of buses. It is approached by another bus manufacturer, Leise Vehicles, who claims that its bus is quieter than Sumo. EBS send its staff to Leise's factory in Germany to collect a sample of data on Leise buses' starting-noise levels. The data for both Sumo and Leise buses' starting-noise levels measured in dB are shown in the GBA Data file. Use Microsoft Excel to summarise separately the two (2) sets of data (under the Noise Level worksheet). Identify the locations and spreads of the samples, each with a measure that takes all data into consideration. Comment on their differences. Present each data in an appropriate type of diagram. Comment on the data distributions

c) Use the Excel summary output in Q1(b) to identify the 95% Confidence Interval (CI) estimate of the mean starting-noise level for each type of bus, and interpret the confidence intervals. Hence infer any differences in the two buses' mean starting-noise levels. State the requirement in using t-distributions to construct the confidence intervals. Justify whether this requirement is met in each case.