possible related topics estimation, simulation, time
Learners could start by listing assumptions that they could make that might help them to simplify the problem. They could time each other walking upstairs and downstairs (is there a significant difference in the time taken?), but they would have to think about those who walk more slowly than themselves.
Places that are on more than one level and that have large numbers of people to get through, such as underground stations (subways) and airports, tend to use a mixture of escalators and lifts (elevators). Escalators can only go so high before you have to get off one and go onto a second, whereas lifts can go much further. But lifts tend to cause queues. There are lots of factors for learners to consider.
© Colin Foster 2012, www.foster77.co.uk