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A contractor combined x tons of gravel mixture that cotained [#permalink]
17 Oct 2007, 18:39

1

This post was BOOKMARKED

00:00

A

B

C

D

E

Difficulty:

(N/A)

Question Stats:

61% (01:43) correct
39% (00:20) wrong based on 48 sessions

A contractor combined x tons of gravel mixture that cotained 10 percent gravel G, by weight, with y tons of a
mixture that contained 2 percent gravel G, by weight, to produce z tons of a misture that was 5 percent gravel G,
by weight. What is the value of X?

hey guys, i got D also, but my approach was a bit different, call it old fashion if you'd like.

I figured from the problem that x=10% gravel (G) y=2%G, and Z=5%G
we know that z=x+y

if we know x=10, therefore 10=10%G, so we find out how much gravel is in the mixture. After we find G, z=5%G, and it proves suff. Same goes for y, also suff, becasue we can find the gravel from it.

How do you guys feel about this approach? Is it dangerous to think it that way?

z/20 = x/10 + y/50
5z = 10x + 2y
Since z = x+y,
5x + 5y = 10x+2y
x = 3y/5

St1:
y = 10. Sufficient. Can solve for x.

St2:
z = 16.

5z = 10x+2y
80 = 10x + 2y

Possible sets:
x = 7, y = 5 (x+y = 12. Out)
x = 6, y = 10 (x+y = 16. In)
x = 5, y = 15 (x+y = 20. Out)
x = 4, y = 20 (x+y = 24. Out)
x = 3, y = 25 (x+y = 28. Out)
....

Re: GMAT Prep DS- Mixture problem [#permalink]
17 Feb 2010, 16:57

I have to give kudos to Killer Squirrel for posting his approach. I am not a math person so the algebraic method makes no sense to me. KS's approach is helping me destroy these problems. Just one questing is there any limitations to this approach?

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