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Problem Solving — algebra and arithmetic (GMAT Focus Edition)
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HELP

by AJWILL » Sat Jul 14, 2012 11:11 am
2001, the closing price of stock A and stock B are the same. 2002, the closing price of two stocks both increased and price of A increased more than the price of B. by what percent was the price increase of stock A greater than the price increase of stock B?

1)2002, the closing price of stock A is 8% greater than the closing price of B
2)The closing price of stock A is increased by 15% from 2001 to 2002

i cant form the equation that is essential to find out the change!!
please help..

all i did was-2001, closing price Stock A = closing price Stock B = x
2002, CP A= 1.08x and CP B=y
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by jdciaravino » Sat Jul 14, 2012 12:41 pm
Remember you don't actually have to calculate the answer only decide if you have sufficient data to do so.

I'm still a newbie when it comes to GMAT quant so this may be wrong(someone please step in and say so if that is the case). Nevertheless I'd rather try and fail then never try But I believe you get the answer by setting up a simple proportion.

115/x ==== 108/100 I just plugged in numbers here(100. I'm assuming A and B were at 100 at closing of 2001) to make things easy. 115 is the price of A in 2002(100+15%). Your trying to figure out the question, 115 is 108% of what number? Since 115 is 8% greater than the closing price of B you get something like 106.5 for B's closing price. And then the answer is the difference? 115-106.5 for roughly a 8.5% change.

Anyway I used both equations here so I guess the answer is C, It can be solved by using both statements together. Someone let me know if I'm completely off base here, still alittle unsure if I'm right
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by eagleeye » Sat Jul 14, 2012 1:00 pm
AJWILL wrote:2001, the closing price of stock A and stock B are the same. 2002, the closing price of two stocks both increased and price of A increased more than the price of B. by what percent was the price increase of stock A greater than the price increase of stock B?

1)2002, the closing price of stock A is 8% greater than the closing price of B
2)The closing price of stock A is increased by 15% from 2001 to 2002

i cant form the equation that is essential to find out the change!!
please help..

all i did was-2001, closing price Stock A = closing price Stock B = x
2002, CP A= 1.08x and CP B=y
Hi AJWILL:
jdciaravino makes a good point. There is no need to actually solve. We just need to know whether the data is sufficient.

Anyway, since you asked : Here are the equations,.

Year Stock A Stock B
2001 x x
2002 y z

statement 1: (y-z)/y = 0.08
statement 2: (y-x)/x = 0.15
And we need to determine (y-z)/x

We don't need to do any math for realizing the answer.
We need to find (y-z)/x. Or in other words we need y/x - z/x.

Statement 1 tells us z/y. We don't know that y/x or z/x is. Insufficient.
Statement 2 tells us y/x. We don;t know what z/x is. Insufficient.

Together we have y/x and z/y. Now y/x * z/y = z/x. So together, we get both y/x and z/x. Hence sufficient.

C is the correct answer as jdciaravino predicted.

Let me know if this helps :)
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