Confidence interval estimates of the proportion of vehicles

Spend some time looking at the vehicles on the road. Look at the first 40 vehicles that drive by. Take note of the number of vehicles that are cars (sedans). Use the data you collect to construct confidence interval estimates of the proportion of vehicles that are cars (rather than trucks, vans, etc.). Report your confidence interval to the group.

Why might people get different results? Is your sample likely a good representation of the total population of all vehicles? Why or why not? Make sure you show all your work and explain each of your steps to arrive at the confidence interval.