Here is an idea that overcomes some of the problems with the classic Add-A-Number effect. Comments and criticism please.
by Bob Farmer
July 22, 2002
I've been thinking about better ways to do the Add-A-Number trick because aside from the potential for addition mistakes, I've always thought predicting the total of some random numbers was rather uninteresting.
So, here's the idea:
Spectator #1 writes down any phone number.
Spectator #2 writes down any phone number.
Spectator #3 crosses out either number.
Spectator #4 then calls out (say) the three numbers from the selected phone number -- the lowest, the highest and the one in the middle (or the lowest digit, the highest digit and the number formed by adding those two together).
This three (or four) digit number is then used to look up a page and entry in a phone book -- and that name and number have been predicted.
Add-A-Number and the tossed-out deck both depend on the participating spectators being ignorant of the values their pals have picked. Thus a participant hears or sees a value which isnt one of his own, he assumes it must have been contributed by one of the others.
For this effect, any switch device can be used, but I prefer the The Forceful Notebook in FEATURE MAGIC FOR MENTALISTS by Will Dexter (Supreme 1974).
Here is the procedure:
1. Spectator #1 is asked to write down any phone number.
2. Spectator #2 then adds a second phone number below the first.
3. Before you hand the notebook to spectator #3, switch sides. He will see your two force phone numbers. Ask him to scratch one out and circle the other one.
Those two numbers have the following characteristics:
(a) Both numbers, though apparently different, are made up of the same numbers. For example, 123-456-7890 and 987-654-3210. This way, when numbers are called out:
(i) If spectator #1 doesnt hear any of his numbers, he will assume they came from spectator #2.
(ii) If spectator #2 doesnt hear any of his numbers, he will assume they came from spectator #1.
(iii) If spectator #3 is a clever bastard and has memorized the number he has chosen, he will assume the numbers called out by spectator #4 come from his number.
(b) Both numbers should use real area codes.
(c) Each number must be written in a different hand.
4. Spectator #4 is then handed the pad and asked to call out the lowest and highest digits and then add those two together to get the third or fourth number.
Alternately, if using a four-way out, you could ask for the highest digit, the lowest digit and any other digit (simply arrange the numbers so there are only 4 possibilities easily done if digits are repeated).
This approach has the advantage of no math and you can tie in the phone book angle.