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# What's that formula again?

## I never could remember how to figure percents this way

#### MatthewHSE

1:04 am on May 23, 2008 (gmt 0)

#### Senior Member

joined:June 9, 2003
posts: 1908

Say I need to know what number 100 is 20% more than, like so:

``x + 20% = 100``

What's the formula to work that out? This is the one part of percentages I never could get right, even five minutes after I had learned it yet again....

The first person to answer this one clearly and concisely shall have the honor of being permanently Scrapbooked [addons.mozilla.org] ;)

[edited by: MatthewHSE at 1:05 am (utc) on May 23, 2008]

#### briggidere

1:17 am on May 23, 2008 (gmt 0)

#### Senior Member

joined:Mar 7, 2005
posts:790

(x / 120) * 100 = y

100/120= 0.8333

0.8333 * 100 = 83.333 (answer)

Test - (83.333 / 100) * 120 = 100

#### wyweb

2:44 pm on May 23, 2008 (gmt 0)

#### Senior Member

joined:Aug 12, 2004
posts:1781

I can never remember that either.

#### ringsoft

6:36 pm on May 23, 2008 (gmt 0)

#### New User

joined:May 16, 2005
posts:29

I've made a note of that so I don't need to remember it.

But I can't remember where I put the note...

#### jecasc

9:28 am on May 24, 2008 (gmt 0)

#### Senior Member

joined:May 8, 2003
posts:1141

Say I need to know what number 100 is 20% more than, like so:

x + 20% = 100

100-20% = x

That was easy...

#### blend27

2:48 pm on May 24, 2008 (gmt 0)

#### Senior Member

joined:Dec 27, 2004
posts:1666

It is not important to know everything, but it is important to know where to look for the answer, as well as how to find the answer. Once one figures out the routine it is fairly easy to apply that formula to pretty much every situation one is faced with... Thus pointers in(to) memory are faster than inline evaluation.

#### MatthewHSE

3:56 pm on May 24, 2008 (gmt 0)

#### Senior Member

joined:June 9, 2003
posts:1908

100-20% = x

That was easy...

I may not have known the right answer, but I knew that was wrong! ;) 20% of 80 is 16, meaning 96, not 100, is 20% more than 80. See briggidere's test case...

#### webfoo

7:53 pm on May 24, 2008 (gmt 0)

#### Full Member

joined:Mar 22, 2008
posts: 315

I don't know... you're MATHew, you should be able to figure this out.

#### topr8

9:26 pm on May 24, 2008 (gmt 0)

#### Senior Member

joined:Apr 19, 2002
posts:3171

to see what 100 is 20% more than

100 / 1.20 ( of course this is the same as 100/1.2 but i use 1.20 to be clear.