Doug Canning's Mental Shopper

Published on Saturday, October 09, 2010 in , ,

Mental Shopper

This is a great effect by Doug Canning, and is presented here with his permission. Practicing and performing it will help you to learn the basics of the Major System so that you know it cold. In the original write-up of this effect (May 1993 Linking Ring), Doug mentions that many people say he just memorized all the prices, but are amazed how he could add them so fast. He doesn't mind, because they're still giving him more credit than he deserves for the work in this effect!


You hand the spectator 5 cards with 6 grocery item and their 3-digit prices on each one. The spectator calls out one item from each card, but not the price. Thanks to your powerful mind, you are able to not only recall the prices of the items, but add them up quickly in your head, as fast as a calculator!

To learn how to do this effect, click here.


Here's how you achieve this amazing feat of memory and math.


Major System


On a separate page, I have included a PDF File (opens in a new window) for you to download, which lists the items and their prices. If you print this file, and use pre-perforated business card (10 to a sheet) stock, you can simply pop out each card individually. Otherwise, just cut up the paper so that you have 10 individual cards. You should now have two complete sets of cards, with cards labeled A through E in each set. One you'll use in the effect, and the other can be a back-up set.


You are going to have your spectator(s) give you one item off of each card, from which you will determine the answer.

There are two methods here, one mathematical and the other mnemonic. First I'll explain the mathematical method. Instead of adding five 3-digit numbers, you're simply going to add five 1-digit numbers. If the spectator were to choose, say, Maalox, Crackers, Bacon, Slimfast, and Tupperware (see PDF File, which opens in a new window), you would simply add the last digit in each price. In this example, you would add 3 plus 7 (which makes 10), plus 9 (making 19), plus 0 (which keep the total at 19), plus 1 (for a final total of 20). This “20” will be the total number of cents in the price.

To find out the number of dollars in the price, simply subtract the number of cents from 50. In the example above, this would mean that the final total is 30 dollars and 20 cents ($30.20). If the final total of the single digits had been, say, 22 cents, the final total would have been $28.22 (because 50-22=28). You'll get prices ranging from $11.39, up to $45.05 in this effect.

Since you're only given the product names, though, how do you know what numbers to add? This is where the basics of the Peg system are going to be put to use. Look carefully at the PDF file (opens in a new window). The phonetic sound that represents the last digit in each price in the peg system (the only number you need to know) is the first sound in the name of the product! For example, the “mmm” sound represents 3 in the phonetic Peg system, so you should instantly know that when the spectator says “Maalox” (which begins with the “mmm” sound) you know to add 3 to your running total. Quick, without looking, can you tell me how much “Vitamins” equals?

To practice this effect, click here.

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