You are trying to estimate the average amount a family spends on food during a year. In the past, the standard deviation of the amount a family has...

You are trying to estimate the average amount a family spends on food during a year. In the past, the standard deviation of the amount a family has spent on food during a year has been  $1200. If you want to be 99% sure that you have estimated average family food expenditures within $60, how many families do you need to survey?