Percents question

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Percents question

by Troika » Sun Jul 31, 2011 4:15 am
One week a certain truck rental lot had a total of 20 trucks, all of which were on the lot Monday morning. If 50 percent of the trucks that were rented out during the week were returned to the lot on or before Saturday morning of that week, and if there were at least 12 trucks on the lot that Saturday morning, what is the greatest number of different trucks that could have been rented out during the week?

(A) 18
(B) 16
(C) 12
(D) 8
(E) 4

(Source: OG Quant Review 2nd Edition, Question 120)

OA: [spoiler](B)[/spoiler]
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by ntamhane » Sun Jul 31, 2011 4:33 am
Let the Number of trucks rented out is x.
Therefore 20-x trucks remain.
50/100 * x truck returned.

"if there were at least 12 trucks on the lot"

Start Substituting x as 18
18 Trucks rented out remain - 2
returned 50% of 18 = 9 therefore total trucks in the lot = 9+2=11 (incorrect as the lot hols at least 12 trucks)

16 Trucks rented out remain - 4
returned 50% of 16 = 8
therefore total trucks in the lot = 8+4=12
Hence [spoiler]16 (B) [/spoiler]is the greatest number of trucks rented out.

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by GMATGuruNY » Sun Jul 31, 2011 4:49 am
HG10 wrote:One week a certain truck rental lot had a total of 20 trucks, all of which were on the lot Monday morning. If 50 percent of the trucks that were rented out during the week were returned to the lot on or before Saturday morning of that week, and if there were at least 12 trucks on the lot that Saturday morning, what is the greatest number of different trucks that could have been rented out during the week?

(A) 18
(B) 16
(C) 12
(D) 8
(E) 4

(Source: OG Quant Review 2nd Edition, Question 120)

OA: [spoiler](B)[/spoiler]
We can plug in the answers, which represent the greatest number of trucks that could have been rented.

Answer choice A: 18 rented.
Trucks left on the lot = 20-18 = 2.
Trucks that are returned = (1/2)*18 = 9.
Trucks on the lot on Saturday = 2+9 = 11.
Too few trucks are on the lot. Eliminate A.

Answer choice B: 16 rented.
Trucks left on the lot = 20-16 = 4.
Trucks that are returned = (1/2)*16 = 8.
Trucks on the lot on Saturday = 4+8 = 12.
Success!

The correct answer is B.
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by Troika » Sun Jul 31, 2011 9:11 am
@ntamhane, @GMATGuruNY: thank you for the solutions!