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asharc
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Gmat Prep DS Question 03 Feb 2008, 09:26
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Hi everyone,

Can someone help me out with this? I got the right answer, but can't understand the right method aside from trial and error.

Much thanks!


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Gmat Prep DS Question 03 Feb 2008, 09:39
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1) \(x + y = 6\)

2) \(0.21x + 0.23y = 130\)

Question if to find \(y\)

1) is not sufficient.

2) By trial and error. 4 and 2 is the only unique solution. So should be B.

I cannot think of any other way. The fact that x and y can only be whole numbers helps in the solution.
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asharc
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Gmat Prep DS Question 03 Feb 2008, 09:41
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Great - thanks. I wanted to make sure I wasn't missing something.
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Gmat Prep DS Question 04 Feb 2008, 15:58
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This type of DS problem really ticks me off. It appears to be C since we need two equations to solve for x (# of 23 cents) and y (# of 21 cents). There must be a way to solve this without using # guessing?

How can one recognize that B works without just randomly trying #s? Is there a pattern? 23x +21y = 130. I don't see anyway to reduce this.
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Gmat Prep DS Question 04 Feb 2008, 17:16
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this is a multiples question where 23A + 21B = 130, where A & B are both integers.

23A = 130 - 21B, plug in 1 for B, see whether that yields an integer value for B. when u find an integer values that make the equation balance, then u found the quantities of each penmcil.
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Gmat Prep DS Question 04 Feb 2008, 17:24
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But bmwhype2....Are you saying everytime I see a two variable equation I should run a test by plugging in #s. What in this question would trigger the bell in your head to begin testing?

Usually, I see a equation like that and figure I need a 2nd equation to solve.
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Gmat Prep DS Question 04 Feb 2008, 17:56
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But bmwhype2....Are you saying everytime I see a two variable equation I should run a test by plugging in #s. What in this question would trigger the bell in your head to begin testing?

Usually, I see a equation like that and figure I need a 2nd equation to solve.
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no. in this case, these variables MUST be integers.

a harder version
7-t55309?hilit=cats+dogs
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Gmat Prep DS Question 04 Feb 2008, 18:38
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bmwhype2, so you are suggesting that when the variables MUST be integers, you run a plugin test? Also, what quant score would you estimate one would start seeing this problem at?
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Gmat Prep DS Question 04 Feb 2008, 19:27
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How can one possibly do this problem in under 2mins?



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