1
$\begingroup$

I need to reverse the effect of subtracting 4% from a large anmount of numbers.

One example: There was subtracted 4% from 100 making it 96. What kind of formula would make it 100 again?

UPDATE:

Above is just an example. For the vast majority of the numbers I only know that 4% was subtracted. Something like this 100 - ((100 / 100) x 4))

Is it possible to do something like we do with Danish VAT:

  • Subtract 20% VAT: 100 x 0.80 = 80
  • Add the 25% VAT back: 80 x 1.25 = 100
  • 0
    Spelling hint: it's `subtract`; the only `s` there is the initial one.2012-12-03

1 Answers 1

4

"$-4$%" means, that you have to multiply with $\frac{96}{100}$. To get the origininal value, you just have to multiply with $\frac{100}{96}$

Edit (Related to your update): It's exactly the same:

  • Subtract 20% VAT means, you have to multiply with $\frac{100-\boldsymbol{20}}{100}=\frac{80}{100} = 0.8$
  • to go back to the original value you have to multiply with $\frac{100}{100-\boldsymbol{20}}=\frac{100}{80} = 1.25$