The Ben Gurion airport terminal in Israel has "moving sidewalk" to speed passengers through a long corridor.
Peter, who walks through the corridor but does not use the moving
sidewalk' takes 150 s to do so. Paul, who simply stands on the moving
sidewalk, covers the same distance in 70 s. Mary not only uses the
sidewalk but walks along it.
How long does Mary take? Assume that Peter and Mary walk at the same speed.