Two Discounts Do Not Make Half Off
A store hangs a sign over its jackets: 30 percent off. A second sign near the register says to take an extra 20 percent off any sale item. Many shoppers add the two together and expect half of the price to disappear. The math does not work that way.
Suppose a jacket costs $80. The first discount is 30 percent of $80, which is $24, so the sale price becomes $56. The extra 20 percent is taken from the new price, not from the old one. Twenty percent of $56 is $11.20, so the final price is $44.80. The shopper saved $35.20, which is 44 percent of the original price, not 50.
There is a quicker way to see this. Paying 70 percent of the price after the first discount means multiplying by 0.70. Paying 80 percent after the second discount means multiplying by 0.80. Multiply the two together and you get 0.56, so the shopper pays 56 percent of the starting price. That leaves a total discount of 44 percent.
The order of the discounts does not change the answer, since multiplication gives the same result either way. What matters is that each percent applies to a different amount, and a percent of a smaller number is a smaller piece. Knowing this helps a shopper compare deals fairly, such as one tag that says 40 percent off against two stacked discounts, and it keeps the final price from being a surprise at the register.