#### Answer

A) 800 car mechanics given the assumptions below

#### Work Step by Step

There are about 800,000 people in San Francisco, as estimated in 2009 by the U.S. Census Bureau. Assume that half of them have cars. If each of these 400,000 cars needs servicing twice a year, then there are 800,000 visits to mechanics in a year. If mechanics typically work 50 weeks a year, then about 16,000 cars would need to be seen each week. Assume that on average, a mechanic can work on 4 cars per day, or 20 cars a week.
For part B, work this out with the population of your own city.