Monday, June 02, 2014

How to use the "WHAT IS NUMBER" T-shirt

I have created T-shirt designs with a mathematical theme, and I sell them on http://www.zazzle.com/mathart.  Lately, I created a magic trick using mathematics and some other tricks for 'guessing' a number that a volunteer has secretly chosen.  Then I adapted this magic trick, in a simpler form, for a T-shirt design.  For those who buy the "WHAT IS NUMBER" T-shirt (or receive one as a gift), here is an explanation of how to use the T-shirt as a magic prop.  To buy the T-shirt, go to http://www.zazzle.com/what_number_magic_shirt-235678841307212061?rf=238851269352169293 (you can customize the shirt.)

You ask a volunteer to choose a number in the range 1 to 144, but to keep it secret. You ask him to find his number on the front of the shirt, and to tell you the letter in the same box as his number. For example, he tells you "U". You ask him to also find his number on the back of the shirt, and to tell you the corresponding letter. While he is finding his number on the back, you translate the "U" to 4, using the mnemonic "foUr", and multiply the 4 by 12, getting 48. He reports "S" for the back, and you translate the "S" to 6, using the mnemonic "Six", and add the 6 to the 48, getting 54. You tell him his number is 54, without (of course) telling him how you derived that number, and he is amazed.
Optionally, you may ask the volunteer to write down his number on a card and to show the card to others nearby.  This allows others to participate by verifying that your 'guess' is correct.  It is obvious that you cannot see the back of the T-shirt, but you should not look down at the front of the T-shirt, either.  Look straight at the volunteer, or the audience, or look up, or close your eyes, or be blindfolded.  The audience may think you have the entire shirt memorized, but that is not necessary.

What is the complete method, and how does it work? The method is based on the following matrix and the cipher that follows.

Matrix of numbers 1 to 144 with rows and columns labelled



B
I
W
H
U
R
S
E
A
N
T
M
B
144
1
2
3
4
5
6
7
8
9
10
11
I
12
13
14
15
16
17
18
19
20
21
22
23
W
24
25
26
27
28
29
30
31
32
33
34
35
H
36
37
38
39
40
41
42
43
44
45
46
47
U
48
49
50
51
52
53
54
55
56
57
58
59
R
60
61
62
63
64
65
66
67
68
69
70
71
S
72
73
74
75
76
77
78
79
80
81
82
83
E
84
85
86
87
88
89
90
91
92
93
94
95
A
96
97
98
99
100
101
102
103
104
105
106
107
N
108
109
110
111
112
113
114
115
116
117
118
119
T
120
121
122
123
124
125
126
127
128
129
130
131
M
132
133
134
135
136
137
138
139
140
141
142
143

The front of the T-shirt indicates which row, and the back of the T-shirt indicates which column. The letters are translated to numbers according to the following cipher. The mnemonics are an aid to memorizing the cipher.

Cipher and mnemonics:


W
2
tWo, first spelled number with W
H
3
tHree, first spelled number with H
A
8
sounds like Ate
T
10
Ten, fourth spelled number with T
I
1
I looks like 1
S
6
Six, first spelled number with S
N
9
NiNe, first spelled number with two N's
U
4
foUr, first spelled number with U
M
11
eleven – Melvin (similar sound)
B
0
B00, surprise, O looks like 0
E
7
sEvEn, first spelled number with two separate E's
R
5
fiveR, slang for 5-dollar bill

After translating the front and back letters to numbers Fr and Bk, calculate this in your head:

Result = 12 * Fr + Bk

You can calculate the 12 * Fr part while the back number is being found.

EXCEPTION: If the Result is zero, change it to 144. 

The Reverse Trick

You can do the magic trick in reverse.  That is, given 54, for example, you can determine where it is found without looking.  You divide 54 by 12, getting the quotient 4 and remainder 6.  Using the cipher, you convert the quotient 4 to U, the position on the front of the shirt, and you convert the remainder 6 to S, the position on the back of the shirt.

Another Trick

For any letter, there is a number that appears under that letter on both the front and the back of the T-shirt.  So you can ask a volunteer to choose a letter, and then you choose a number that appears under that letter on both the front and the back.  To do this, it will help to be familiar with the multiples of 13.  (Most people are not, and as a result, think that 91 is a prime number.)

Given a letter, use the cipher to convert the letter to a number, then multiply the number by 13.  For example, suppose the letter is E.  According to the cipher, the corresponding number is 7.  7 times 13 is 91, so you declare that 91 is found in box E on both the front and the back of the T-shirt.

The equivalence of 0 and 144 applies to all tricks.