ESCALATOR EXERCISE*
When Mr Watson was feeling lazy he would stand on the escalator and let it carry him to the top, taking 40 seconds. When he was feeling a bit more energetic, he would walk up the escalator at two steps a second, and would reach the top twice as quickly as if he had just let the escalator carry him up.
How long is the staircase? In other words, how many steps can be seen on the escalator at any one time?