vinay1983 wrote:Barry walks from one end to the other of a 30-meter long moving walkway at a constant rate in 30 seconds, assisted by the walkway. When he reaches the end, he reverses direction and continues walking with the same speed, but this time it takes him 120 seconds because he is traveling against the direction of the moving walkway. If the walkway were to stop moving, how many seconds would it take Barry to walk from one end of the walkway to the other?

A.48
B.60
C.72
D.75
E.80

Let W = Speed of walkway in METERS per MINUTE
Let B = Barry's normal walking speed in METERS per MINUTE
So, B+W = Barry's net speed when he's walking WITH the walkway, and B-W = Barry's net speed when he's walking AGAINST the walkway.

Barry walks from one end to the other of a 30-meter long moving walkway at a constant rate in 30 seconds, assisted by the walkway.
Traveling 30 meters in 30 seconds, is the same as traveling 60 meters in 60 seconds (i.e., 1 minute).
In other words, B+W = 60 meters per minute

...it takes Barry 120 seconds because he is traveling against the direction of the moving walkway.
Traveling 30 meters in 120 seconds, is the same as traveling 15 meters in 60 seconds (i.e., 1 minute).
In other words, B-W = 15 meters per minute

We have:
B + W = 60
B - W = 15
Add the two equations to get 2B = 75
Which means B = 75/2 = 37.5
In other words, Barry's normal walking speed is 37.5 meters per minute.

If the walkway were to stop moving, how many seconds would it take Barry to walk from one end of the walkway to the other? (a distance of 30 meters)
Time = distance/speed
= 30/37.5
STOP
Notice that 30/37.5 evaluates to be less than 1, which means it will take less than 1 minute for Barry to travel 30 meters.
Since only 1 answer choice is LESS THAN 1 minutes, the correct answer must be A

Cheers,
Brent