I'm having a brain fart today and can't figure out something.

I have the formula: x + 20% = y Which can be expanded to: x + ((x / 100) * 20) = y What I'm trying to do is find out what x is when I know what y is.

Here's a simple (and probably unneeded) example:

If y is 120 then x is 100 since 20% of 100 is 20 and 100 + 20 = 120 . x + 20% = 120 , x = 100 .

I have made myself a spreadsheet for reference so I can get the answers but I'm trying to remember how to reverse the formula. If anyone could help it would be appreciated and I'm sure any maths students may appreciate it too.

EDIT: The spreadsheet requires me to put in what x might be and it'll give me a range form the number I input and up by 400 rather than me putting in y to find out x meaning I need to scroll down until I find the answer.

Edited by Borzoi: Clarification

7 Years
Discussion Span
Last Post by Borzoi

Nevermind, I remembered.

It's a matter of dividing y by 1.20 I remembered that another way to write the original formula would be x * 1.20 = y so it's much easier to reverse engineer into y / 1.20 = x .

For different percentages you would change the .20 part to the percent. For example, for 4% you would use 1.04 and for 17.5% you would use 1.175 .

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