# An embarrassingly easy math question: How to calculate a 15% difference?

**URL:** <https://boards.straightdope.com/t/an-embarrassingly-easy-math-question-how-to-calculate-a-15-difference/695577>\
**Category:** Factual Questions\
**Created:** [August 15, 2014, 2:26am UTC](https://boards.straightdope.com/t/an-embarrassingly-easy-math-question-how-to-calculate-a-15-difference/695577 "2014-08-15T02:26:47Z")\
**Posts on this page:** 2\
**Page:** 2

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**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\
**Post date:** [August 16, 2014, 2:06am UTC](https://boards.straightdope.com/t/an-embarrassingly-easy-math-question-how-to-calculate-a-15-difference/695577/21 "2014-08-16T02:06:30Z")

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> [@](#):
>
> Quoth **choie** :
> 
> This is a place where documents include a table with three figures: 1.1, 1.0 and 1.0, and the total was given as 3.4. They’re likely either rounding things way up or down, which is fine, but you have to include that rounding in both the total and the figures being added together, duh.

There are no possible numbers that round that way. 1.1 is at most 1.15, and 1.0 is at most 1.05, so the total of those three numbers should be at most 3.25. Even if the numbers are _exactly_ something-five, and even if you improperly round 5s up sometimes and down sometimes, the rounded value of the sum should be at most 3.3 . The only way I can think of to get those numbers is if some of the numbers are actually truncated and some are rounded, but that’s all kinds of wrong.

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**Author:** ![Isilder](https://avatars.discourse-cdn.com/v4/letter/i/cc9497/32.png) [@Isilder](https://boards.straightdope.com/u/Isilder)\
**Post date:** [August 16, 2014, 3:14am UTC](https://boards.straightdope.com/t/an-embarrassingly-easy-math-question-how-to-calculate-a-15-difference/695577/22 "2014-08-16T03:14:40Z")

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[quote=“dracoi, post:19, topic:695577”]

Is it possible the 15% difference is a difference in tax rate or after-tax yields or something, /QUOTE]  
When they say the difference between A and B is 15%,  
it may be that the process was to deduct 15% from B. You might be able to assume this where B is before tax and A is after tax…depending on exactly what is being done.

Previously the discussioned assumed that the 15% was 15% of A.  
It might also be the before and after of adjusting _something else_ 15% - 15% more tax payers , for example.

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