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by sparkle6 » Mon Sep 26, 2011 10:58 pm
The moving walkway is a 300 foot long walkway consisting of a coveyor belt that moves continuously at 3 feet per second. When Bill steps on the walkway, a group of people that are also on the walkway stand at 120 feet in front of him. He walks toward the group at a rate of 3 feet per second. Once Bill reaches the group of people, he stops walking and stands with them until the walkway ends. What is Bill's average rate of movement for his trip along the moving walkway?

a. 2 ft/sec
b. 2.5 ft/sec
c. 3 ft/sec
d. 4 ft/sec
e. 5 ft/sec

Seems like a tough question. Anyone know how to solve?
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by chetansharma » Mon Sep 26, 2011 11:18 pm
IMO the answer is E

The time taken by bill to reach the group will be 40 sec and his effective speed for this distance is 6 ft/sec
With in this 40 sec, he would have traveled 240 ft.
So for the remaining 60 ft, at 3ft/sec, he would take 20 sec.

So the avg speed can be calculated as ((6*40)+(3*20))/(40+20) = [spoiler]5ft/sec[/spoiler]

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by gmatboost » Tue Sep 27, 2011 9:43 pm
That's correct. You could also say that:

He reaches the others in 120/3 = 40.
At that point, had gone 40*6 = 240 feet.
To go the last 60 feet takes 60/3 = 20 seconds.

Total distance: 300 feet. Total time: 60 seconds.
Average Rate: [spoiler]300/60 = 5 ft/s.[/spoiler]
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