Stupid Algerbra Questions : GMAT Quantitative Section
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# Stupid Algerbra Questions

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10 Aug 2010, 11:37
I have to solve this for Y. Here are the steps that I took where did I go wrong.

$$100-y=\frac{100,000}{(100+x)}$$
Subtract 100 from both sides
$$-y=\frac{100,000}{(100+x)}-100$$

multiply both sides by -1
$$y=\frac{-100,000}{(100+x)}+100$$

The anser given is
$$y=100-\frac{100,000}{(100+x)}$$

Are these the same things if this were so then

7-6
would eauly
-7+6 which it does not

Where am I going wrong

Last edited by bb on 10 Aug 2010, 12:21, edited 2 times in total.
formulas
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10 Aug 2010, 12:03
Where are our mathematicians )
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10 Aug 2010, 12:21
I have put it into a readable format with formulas.
What is the source of this question?
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10 Aug 2010, 12:40
The two expressions for y are equivalent due to the commutative property of addition (a + b = b + a and in this case a = 100 and b = the fraction including the negative sign). The two expressions involving 7 and 6 are not analogous to the two expressions involving 100 and the fraction.
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10 Aug 2010, 16:38
Quote:
multiply both sides by -1
y=$$\frac{-100,000}{(100+x)}+100$$

The anser given is
y=100-$$\frac{100,000}{(100+x)}$$

Are these the same things if this were so then

7-6
would eauly
-7+6 which it does not

Where am I going wrong

y in the both of the above scenario is the same if we keep x as a variable. 7-6 is not same as -7+6 since we know the exact value of each of the numbers.

The value of y in the above scenario depends on the value of x. If x is zero then y would be negative, if x >= 999900 then y is positive.

Hope I have not confused you further
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10 Aug 2010, 17:46
7-6 = -6+7
this is right. You have just changed the order of the numbers.

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Re: Stupid Algerbra Questions   [#permalink] 10 Aug 2010, 17:46
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