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stuckkk!!!inverse function

Problem Solving — algebra and arithmetic (GMAT Focus Edition)
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Source: — Quantitative Reasoning |
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by garuhape » Mon Feb 21, 2011 7:57 am
At the moment you have the normal function, that means y equals something:

y=5/4x+8.2

The inverse function is always x equals something.

Therefore it is in this case:

x=(y-8.2)*4/5 = 4/5y-6/14/25
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by Tani » Mon Feb 21, 2011 6:46 pm
To find an inverse function, substitute y for g(x) then solve for x. Then switch x and y

y = { ( x/4+ 6) /5 } +7

first multiply everything by 5 to get rid of that fraction.

5y = (x/4 + 6) + 35
5y = x/4 + 41

now multiply by 4 to get rid of the other fraction
20y = x + 164

x = 20y - 164

now switch

y = 20x + 164
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by rohu27 » Mon Feb 21, 2011 7:02 pm
Tani Wolff - Kaplan wrote: x = 20y - 164

now switch

y = 20x + 164
Tani,

it shud be y=20x-164? why are we inverting the sign here?
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by Tani » Tue Feb 22, 2011 9:05 am
WE are inverting the sign because I'm a lousy typist - in other words - we don't ! sorry :-)
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by yellowho » Sun Feb 27, 2011 5:19 pm
Is this within the test subject of gmat?
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by Tani » Sun Feb 27, 2011 5:42 pm
I haven't seen one on a released GMAT problem, but I run into them on the SAT so I assumeone could show up. They are not tough if you attack them systematically. Don't let them freak you out.
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