Comments on: Reverse my percentage?
http://ask.metafilter.com/139979/Reverse-my-percentage/
Comments on Ask MetaFilter post Reverse my percentage?Sun, 06 Dec 2009 19:28:26 -0800Sun, 06 Dec 2009 19:28:26 -0800en-ushttp://blogs.law.harvard.edu/tech/rss60Question: Reverse my percentage?
http://ask.metafilter.com/139979/Reverse-my-percentage
How do you find a number that minus a percentage of itself is a certain number? <br /><br /> What would be the formula (in a spreadsheet like pages.app) to find that 100 - 20% = 80, if you only know the percentage and the result (in this example 20% and 80) <br>
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I've tried googling this but I don't think I know the name or term of what I'm looking for, reverse percentage doesn't seem right...post:ask.metafilter.com,2009:site.139979Sun, 06 Dec 2009 19:25:28 -0800JulianDaymathpercentagesexcelformulaspreadsheetBy: mpls2
http://ask.metafilter.com/139979/Reverse-my-percentage#2001947
X * 0.8 = 80<br>
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X = 80 / 0.8comment:ask.metafilter.com,2009:site.139979-2001947Sun, 06 Dec 2009 19:28:26 -0800mpls2By: mpls2
http://ask.metafilter.com/139979/Reverse-my-percentage#2001949
To be more precise...<br>
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X * (1 - 0.2) = 80<br>
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X = 80 / (1 - 0.2)comment:ask.metafilter.com,2009:site.139979-2001949Sun, 06 Dec 2009 19:29:26 -0800mpls2By: Deathalicious
http://ask.metafilter.com/139979/Reverse-my-percentage#2001951
An easier way is to remember that subtracting a percentage is the same as multiplying by a fraction. In the case of 20%, that is 8/10 (x-20% = x * 8/10). <br>
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That makes the problem much easier to solve.<ul><li>x - 20% = 80</li><li>0.8x = 80</li><li>x = 80 / 0.8</li></ul><br>
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So the general formula is result/((100-percentage)/100)comment:ask.metafilter.com,2009:site.139979-2001951Sun, 06 Dec 2009 19:33:54 -0800DeathaliciousBy: JulianDay
http://ask.metafilter.com/139979/Reverse-my-percentage#2001953
Thanks so much.comment:ask.metafilter.com,2009:site.139979-2001953Sun, 06 Dec 2009 19:33:58 -0800JulianDayBy: msittig
http://ask.metafilter.com/139979/Reverse-my-percentage#2001960
Use this to turn the word problem into an equation:<br>
"of" is * (multiplication)<br>
"is" is = (the equality sign)<br>
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Example:<br>
$43 is 90% (10% off) of what?<br>
43 = 0.90 * x<br>
x = ...comment:ask.metafilter.com,2009:site.139979-2001960Sun, 06 Dec 2009 19:41:45 -0800msittigBy: TravellingDen
http://ask.metafilter.com/139979/Reverse-my-percentage#2001963
I was going to work it all out, but then just thought, hey, why not work it out as a normal algebraic statement and feed it to wolfram alpha.<br>
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http://www.wolframalpha.com/input/?i=x+-+%28x*%2820%2F100%29%29+%3D+80comment:ask.metafilter.com,2009:site.139979-2001963Sun, 06 Dec 2009 19:46:09 -0800TravellingDenBy: eafarris
http://ask.metafilter.com/139979/Reverse-my-percentage#2002181
I may have learned only one thing in middle school math, but it was this formula:<br>
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"Percent over 100 = 'is' over 'of'."<br>
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Cross multiply and divide to solve for the unknown.comment:ask.metafilter.com,2009:site.139979-2002181Mon, 07 Dec 2009 06:05:09 -0800eafarris