Add a percentage, say 5% is not making an addition. It is a multiplication by (1+5/100). You may also multiply by 5, divide by 100, and then add the result to the original amount.

For instance, the VAT of 20% multiplies the taxes free amount by 1.2, or else adds 20% of the taxes free amount to itself.

That's why the VAT amount of 20% is NOT 20% of the price, as the price is the taxes included amount. To obtain the VAT amount from the price, you must first DIVIDE the price b...