# Math Help - Percentages

1. ## Percentages

Hi al. I have a problema. I know it is possible with a very simple operation. This is the problema: I have a value, I want to add a percentage to it, and then remove that percentage but now of the new value and keep the original value: if I have 100, add 15%, it gives me 115, but now if I take the 15% of the 115, I have 97.75. I want the formula to add the initial 15% in such way that I can take 15% of the total value and keep the original 100. Any help please? Regards Virginio Reis P.S. Some how the fórum does not accept the carriage return, so the post goes in a single line.

2. ## Re: Percentages

Let's call the starting value 'x'
Let's call the final value 'y'

x * 1.15 will give you the 115% (your 115 value)

(x * 1.15)*(0.85) will give you 15% off the value of 115% (your 97.75 value)

So, you can write the expression as:
1.003x = y

What you seem to be asking for is bizarre, as you would simply be multiplying by 1.

$\frac{x\times 1.15}{1.15}=x$

3. ## Re: Percentages

Is not bizarre. Supose you have a business and a guy help you on selling something, but you have to give him/her a 10% comission. You want to keep the original value for yorself and past the comition for the customer. I foud the solution meanwile: 100/0.9 = 111.11. Now 10% of 111.11 is 11.11. 111.11 - 11.11 = 100. There it goes. You give the vendor the comission and you keep your money.