nitzz 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
As this is a Rates & Work problem, we should use a chart to keep track of the different legs of the journey. We will need a row for the journey walking with the walkway and one for the journey against.
The distance traveled for each leg of the journey was 30 meters. We also have the time each trip took. The only unknown is the rates for each leg of the trip. There are really two unknowns: The rate at which Barry walked, and the rate at which the walkway moved. Label the rate Barry walked b, and the rate at which the walkway moved w:
Distance = Rate × Time
With walkway 30 = b + w × 30
Against walkway 30 = b – w × 120
This allows us to create two equations:
30 = 30(b + w) ⇒ 30 = 30b + 30w
30 = 120(b – w) ⇒ 30 = 120b – 120w
We now have enough information to solve for b and w. The question asks for the time it would take Barry to walk the distance by himself, so we want to solve for b. We can solve for b with Combination. Multiply the first equation by 4 and add the equations together:
120 = 120b + 120w
+ 30 = 120b – 120w
150 = 240b
Now we can solve for b:
Now we have one final equation to solve. How long did it take Barry to walk 30 meters?