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Does this common math misunderstanding have a name?

3 点作者 HappyFunGuy超过 9 年前
Not getting a 33 percent discount is the same as paying about 50 percent more.<p>A 33 percent discount on a 100 dollar item makes the price 67 dollars. Not getting the discount makes the price go from 67 to 100, an increase of 33 dollars, which is a 49.25 percent increase.<p>While we&#x27;re at it, is there a name for when people tell you meaningless things like, &quot;I doubled my sales&quot;, only to discover the sales went from 1 unit to 2. It&#x27;s an error so common that I imagine it must be named by now.

6 条评论

s_dev超过 9 年前
&quot;While we&#x27;re at it, is there a name for when people tell you meaningless things like, &quot;I doubled my sales&quot;, only to discover the sales went from 1 unit to 2. It&#x27;s an error so common that I imagine it must be named by now.&quot;<p>Don&#x27;t know if it has a word but it has its own xkcd comic.<p><a href="https:&#x2F;&#x2F;xkcd.com&#x2F;1102&#x2F;" rel="nofollow">https:&#x2F;&#x2F;xkcd.com&#x2F;1102&#x2F;</a>
andyjohnson0超过 9 年前
I&#x27;m not quite sure what you&#x27;re asking, but one way that fractions (and by extension, ratios) are tricky is that a larger denominator gives a smaller value. Five is greater than three but a fifth is smaller then a third. I&#x27;ve seen my children struggling with this.<p><i>&quot;It&#x27;s an error so common that I imagine it must be named by now.&quot;</i><p>Not really an error so much as an attempt to mislead.
评论 #10386133 未加载
HappyFunGuy超过 9 年前
This list is rather daunting to check for a match against this example: <a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;List_of_cognitive_biases" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;List_of_cognitive_biases</a> It&#x27;s either in this list, or we should describe this bias as new?
HappyFunGuy超过 9 年前
If we don&#x27;t discover a name, I guess we could call the first one the &quot;Small discount, large increase equivalence?&quot; sounds pretty bad. Anything with the word numerator or denominator in it would be far worse.<p>On the second one, &quot;unqualified percentages?&quot;
DanBC超过 9 年前
A good example of &quot;I doubled my sales&quot; would be &quot;My risk of getting cnacer has doubled&quot; - this might mean my risk has gone from 1 in 100,000 people to 2 in 100,000 people.
HappyFunGuy超过 9 年前
I found the answer. It is called the Framing effect. <a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Framing_effect_(psychology)" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Framing_effect_(psychology)</a><p>I would posit that there could be benefit in naming the more specific form of discount&#x2F;increase, as its hard to derive benefit from the knowledge of a general &quot;framing effect&quot; as framing is more often non numerical.