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 Post subject: GRE Speed / Distance / Time (Select One)
PostPosted: Fri Dec 03, 2010 3:30 pm 
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Joined: Sun May 30, 2010 3:15 am
Posts: 424
Tim traveled 40 percent of the distance of his trip alone, continued another 20 miles with Sam and then finished the last half of the trip alone. How long was the trip?

A. 50 miles
B. 100 miles
C. 160 miles
D. 200 miles
E. 240 miles

(D) The easiest way to visualize this problem is to turn it into an equation. Let x be the total length of the trip. We then know that this is what Tim traveled:
0.4x (first part of the trip traveled alone) + 20 (miles traveled with Sam) + 0.5x (last leg of the trip traveled alone).

Thus, 0.4x + 20 + 0.5x = x. Now solve for x:
0.4x + 20 + 0.5x = x
0.9x + 20 = x
20 = 0.1x
200 = x.

The total length of the trip was 200 miles. The answer is (D).
questions or comments.
-------------

How did you get 5x?


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 Post subject: Re: math (test 5, question 32): time / speed / distance
PostPosted: Fri Dec 03, 2010 3:47 pm 
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Joined: Sun May 30, 2010 2:23 am
Posts: 498
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There is no 5x in the solution.

We denote the whole distance by x. Therefore each part of the distance is less than x (some fraction of it).

"Tim traveled 40 percent of the distance of his trip alone,"
0.4x

"continued another 20 miles with Sam"
20 miles

"and then finished the last half of the trip alone."
0.5x

The resulting equation is:
0.4x + 20 + 0.5x = x.


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