# A little math/excel help

**URL:** <https://boards.straightdope.com/t/a-little-math-excel-help/428087>\
**Category:** Factual Questions\
**Created:** [November 28, 2007, 9:40pm UTC](https://boards.straightdope.com/t/a-little-math-excel-help/428087 "2007-11-28T21:40:27Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![Zebra](https://avatars.discourse-cdn.com/v4/letter/z/c0e974/32.png) [@Zebra](https://boards.straightdope.com/u/Zebra)\
**Post date:** [November 28, 2007, 9:40pm UTC](https://boards.straightdope.com/t/a-little-math-excel-help/428087/1 "2007-11-28T21:40:27Z")

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I’m working on a spreadsheet and I can’t quite figure out the formula.

Column A has a price in it. The price is column B plus 13%. So B is the original cost, A is the cost that has been marked up 13%.

A=B+(B\*13%)  
The thing is I know the marked up price but not the original price. I need a formula to turn the 113% price into the 100% price.  
Any ideas?

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**Author:** ![jk1245](https://avatars.discourse-cdn.com/v4/letter/j/49beb7/32.png) [@jk1245](https://boards.straightdope.com/u/jk1245)\
**Post date:** [November 28, 2007, 9:44pm UTC](https://boards.straightdope.com/t/a-little-math-excel-help/428087/2 "2007-11-28T21:44:53Z")

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Wouldn’t it be the marked up price divided by 1.Markup percentage?

In your example, it would be 113/1.13

Or are you saying you don’t know the percentage either?

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**Author:** ![brewha](https://avatars.discourse-cdn.com/v4/letter/b/91b2a8/32.png) [@brewha](https://boards.straightdope.com/u/brewha)\
**Post date:** [November 28, 2007, 9:46pm UTC](https://boards.straightdope.com/t/a-little-math-excel-help/428087/3 "2007-11-28T21:46:05Z")

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in the column for B

=(1/1.13)\*A

Why wouldn’t that work? Or am I misunderstanding the question?

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<div class="post-metadata">

**Author:** ![Zebra](https://avatars.discourse-cdn.com/v4/letter/z/c0e974/32.png) [@Zebra](https://boards.straightdope.com/u/Zebra)\
**Post date:** [November 28, 2007, 9:47pm UTC](https://boards.straightdope.com/t/a-little-math-excel-help/428087/4 "2007-11-28T21:47:18Z")

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I know the percentage, it’s 13.  
You’ve got it. Thanks, I just couldn’t get my brain into math mode this afternoon.

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**Author:** ![rowrrbazzle](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rowrrbazzle/32/414_2.png) [@rowrrbazzle](https://boards.straightdope.com/u/rowrrbazzle)\
**Post date:** [November 28, 2007, 9:47pm UTC](https://boards.straightdope.com/t/a-little-math-excel-help/428087/5 "2007-11-28T21:47:28Z")

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algebraically:

a=b+b\*13%

'(100% of b is b)

a=b_100% +b_13%

a=b\*113%

'divide both sides by 113%

a/113% = b

b = a/113%

or

b = a/1.13

Plug a few numbers in so you can see that it works.