You are in a line at the bank drive-through and 3 cars are in front of you. You estimate that the clerk is taking about six minutes per car to serve. How long do you expect to wait in line?

I will wait in line for about 18 minutes

Explanation:

If I am in a line at a bank drive through and 3 cars are in front of me and the clerk is taking about 6 minutes per car to serve, the number of minutes I should expect to wait in line can be computed as follows:

Since the clerk uses 6 minutes to serve a single car, their are 3 cars before me. This means the clerk will serve those 3 cars before me. Mathematically,

if 1 car uses 6 minutes

3 car will use? minutes

cross multiply

3 * 6

3 * 6 = 18 minutes

I will wait in line for about 18 minutes