Question

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

Answer 1

47.7 seconds to the nearest tenth.

Explanation:

Let peters speed be Ps , the Sidewalks speed be Ss and Mary's speed be Ps.

(equal to Peters) and let the distance they all walk be x :

Then Px = x/150 , Ss = x/70

Mary's speed = Ss + Ps:

So Ps + Ss = x/t where t is the time Mary Takes.

x/150 + x / 70 = x/t

((70x + 150x) / (150*70) = x / t

220x / (150*70) = x / t

220 / 150*70 = 1 /t

t = 150*70 / 220

t = 47.7 second.