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Posted by Kimmo Laine on 09/01/06 08:16
"universalbitmapper" <jbmorla@gmail.com> wrote in message
news:1157093880.725466.161370@h48g2000cwc.googlegroups.com...
> Hi,
>
> I'm coding a PHP/MySQL application.
> I'm looking for the formula to compute the original variable after it
> has been applied VAT.
> For instance 100 + 18% -> 118.
> But if I try to find out 100 from 118 - 18%, the result is greater than
> 100.
> I don't have enough maths background to solve the equation:
> c = a + (a*b/100)
> I'm stuck at this point:
> a = (a*b/100) -c
> I would like to have all 'a' on the left side and b and c on the right.
>
> Can someone help?
Short answer:
100 / (100+VAT) * price with VAT = original price
100 / (100+18) * 118 = 100
I don't know the correct mathematical terms, but basicly this is what
happens:
the ratio of 100 : (100 + VAT) must be the same ratio as "original price" :
"VAT price"
100 / (100 + VAT) = original price / VAT price
multiply both sides with VAT price:
==> 100 / (100 + VAT) * VAT price = original price * (VAT price/VAT price)
==> 100 / (100 + VAT) * VAT price = original price
there you have it.
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