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# How to calculate the tax percentage of a purchase without knowing the tax rate?

I want to find out what percentage of tax was applied to the end price of $48.14. Before tax the price was $42.98.

If I do "42.98x100/48.14" the answer is 89.28% which would mean that the price was $42.98 + 10.72% . However, that's incorrect!

Even rounding to the nearest whole number brings it to 11%.

I actually know that the answer is 12% and I confirm it by calculating $42.98 x 1.12 = $48.14

Even though I know the answer in this case, I want to know how to simply calculate the sales tax on an item without knowing the tax rate, only knowing the before and after prices.

What am I doing wrong?

### 3 Answers

- 9 years agoFavorite Answer
Algebra let A= 42.98

let Pprice= 48.14

let Tx = tax rate

Then A+{A(Tx)}=Pprice

Then A(Tx)= Pprice-A

Follows (Tx)= (Pprice-A)/A

Sub Tx= (48.14-42.98)/42.98

Tx=5.16/42.98

Tx= 0.12 --> 12%

- DavidLv 79 years ago
42.98 + 42.98x = 48.14

42.98x = 5.16

x = 5.16 / 42.98

x = 0.12005583992554676593764541647278

12.01%

12% to the nearest whole number