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OG DS #57

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Source: — Data Sufficiency |
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by chatekar » Wed Jul 18, 2007 7:52 am
erdnah,

To find the value of 1/X + 1/Y i.e. (X+Y)/XY, so you need two things,
first is X+Y and the second is XY.

Both are given in statement 1 and 2 so you need both the statements together.

Hope this helps

Thanks
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by erdnah » Wed Jul 18, 2007 7:55 am
@chatekar, yeah, i found that information also in the og :)

but what i really want to know is, why i can't multiply the last term with xy, so that i would get x+y = 0!? i feel terrible stupid :x
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by chatekar » Wed Jul 18, 2007 8:27 am
If you are multiplying by xy to get the value of the given expression, then you are changing the value of the given expression.
You can't simply multiply by xy, you also need to divide by xy so that value of the expression doesn't change.

Am I making sense?

Thanks
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by erdnah » Wed Jul 18, 2007 10:59 am
Yeah, of course you do... :roll:
There are days, I should have stayed in bed. :wink:
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OG DS #56

by erdnah » Fri Jul 20, 2007 9:32 am
It seems as if I did the same mistake today again :roll:

When there is x = x², I divided both sides by x. I though I would get 1 = x which seemed to be wonderful in my eyes... but x could also be 0!

What was this time (or as on the problem above) my mistake in thinking?

Hope someone can help me..
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Re: OG DS #56

by bingojohn » Tue Aug 07, 2007 10:59 am
erdnah wrote:It seems as if I did the same mistake today again :roll:

When there is x = x², I divided both sides by x. I though I would get 1 = x which seemed to be wonderful in my eyes... but x could also be 0!

What was this time (or as on the problem above) my mistake in thinking?

Hope someone can help me..
Solve equation:

x^2 = x
x^2 - x = 0
x(x - 1) = 0

x = 0 OR x = 1

hope this helps...
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