Enter an original price and a discount to get the price you will actually pay and the amount saved. You can also stack discounts to see what "extra 20% off sale prices" really comes to, or work backwards from the ticket price to the percentage off.
"30% off, plus an extra 20% off sale prices" reads like 50% off. It is not. The second discount applies to the already-reduced price, so you pay 0.7 x 0.8 = 56% of the original - a 44% saving. The gap widens as you stack more: three 20% discounts give 48.8% off, not 60%.
To find the discount from two prices, divide the saving by the original price. Dividing by the sale price instead inflates the figure, which is a trick worth recognising in advertising.
They multiply rather than add. 30% off followed by an extra 20% off leaves 0.7 x 0.8 = 0.56 of the original price, so 44% off in total, not 50%.
Subtract the sale price from the original, divide by the original, and multiply by 100. From 80 down to 60 is (80-60)/80 = 25% off.
Steuervergleich Kanton Zürich — Gemeindesteuern vergleichen (Deutsch)