How many pennies are in a shopping mall?

This is a relatively common interview question. It seems more important to discuss your process of thinking rather than coming up with an actual answer. Let's say the average shopping mall has 3 floors and 50 small stores/kiOSks per floor. There are likely about 3 or 4 department stores as well. Maybe every regular store has 3 cash registers and each department store has 15. If all of these cash registers have on average 100 pennies in them (and maybe some backup rolls in storage--let's say 400 pennies), then in the stores alone there are 105,000 pennies. Now we have to consider the humans in the mall. Let's say there are 1,000 people in this mall and the average person has 5 pennies on them (they're not a popular currency and children likely have no change on them.) Then humans alone would account for 5,000 pennies in the store. This would bring the total to 155,000 pennies in the mall. There are certainly other factors you might want to bring up, however. If the mall has a food court, this would account for a lot more cash registers, but fewer stores on one floor. If it's near a holiday, there certainly would be an increased number of people shopping. This question shows that you can think creatively and critically.