As Herberger's closing sale winds down, you'll want this simple math tip

The sign at Herberger's entrance on Thursday said "Last 12 days," which means the stores are likely closing around Aug. 26 or so. Nearly everything is now 70 to 90% off with an extra 10, 20 or 30 percent discount.

So does that mean that a sweater marked 90% off plus an additional 10% off is free? Unfortunately, no.

Some bargain hunters may not be aware that additional discounts cannot be added together. For example, if a $100 sweater is discounted 90%, the new price is $10. The additional 10% discount is deducted from the $10 subtotal, which is $1. So a $100 item marked down 90% and 10% would cost $9.

Retailers use Americans' fuzzy math to make a deal seem better than it is. A BOGO or "buy-one-get-one" offer is a good example of that. Initially, a BOGO usually meant that a consumer bought one item and got an identical second one free, a 50% savings. Then it began to change to "buy one and get another at 50% off." To some, that may sound like getting 50% off if two items are purchased. It's actually 25% off each because the first item is sold at full price and the second item is 50% off.

For example, say a $10 bottle of detergent is on a 50% off BOGO. The first bottle is at $10 (regular price) and the second bottle is $5 (50% off $10). The total for both is $15 on a BOGO sale, regularly $20. That's only a 25% discount ($5) on the two bottles ($20 X .25= $5).