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GreatMathematicians BlaisePascal
LeonardoFibonacci
DavidHilbert
IsaacNewton
Archimedes
WhosNext???
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ArthurT.Benjamin BachelorofSciencefromCarnegieMellon
PhDfrom
Johns
Hopkins
ProfessoratHarveyMudd
Mathemagician
Presentationsaroundtheglobe
Advancedcalculations
Mathematicalagility
AmericasBestMathWhiz ReadersDigest
NottobeconfusedwithArthur Benjamin
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HisPresentationMentallymultiply
large
numbers
Mentallysquarefive
digitnumbers
MemorizePi
to
one
hundreddigits
MasterofPhonetic
Code
Andmore!
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Mathemagics
Mentalmath
Mathtricks:
Pickanumber
Whoa! Takeiteasy,makeit1or2digits
Doubleit
Add12
Divide
by
2
Subtractoriginalnumber
Isthenumber
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WhyEveryNumberAlwaysGoesTo6
Yournumberisx
Double
it:
2xThenadd12:2x+12
Thendivideby2:(2x+12)/2=x+6
Thensubtract
the
original
number:
x+6 x
=6
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Magical1089Pickathreedigitnumber(withthe
digitsdecreasing)
Reversenumber
Subtractreverse
fromoriginal
Callthisnewanswer:AnswerX
AddAnswer
X
to
the
reverseofAnswerX
Does it equal 1089?
If not, you made a mistake!
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WhyEveryNumberAlwaysGoesTo108abc = 3 digit number
This equals: 100a + 10b + c
cba = reverse of 3 digit numberThis equals 100c + 10b + a
Subtracting cba from abc equals:
(100a + 10b + c) (100c + 10b + a)
= 100(a - c) + (c a)
= 99(a-c)
We now receive one of the following multiples of 99:
198, 297, 396, 495, 594, 693, 792, 891
Adding the reverse of any of these numbers produces the answer 1089
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Multiplyingby11Twodigitnumber
Steps:Addthedigits
Placein
between
the
digits
Exceptiontotherule:
Ifsumisgreaterthan9
Addthe
digits
Placesecondnumberinbetweenthedigits
Addthe
1to
the
first
digit
of
the
new
number
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SquaringNumbersThatEndin5 Multiply first digit (or all digits but the last
one for three digit numbers or more) by nexthighest number
Place 25 at the end of new number Example: 25 x 25
2 x 3= 6
25 x 25= 625
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MemorizingDates Monday-1
Tuesday-2
Wednesday-3
Thursday-4
Friday-5
Saturday-6 Sunday-7 or 0
January-6*
February-2*
March-2
April-5
May-0
June-3
July-5
August-1
September-4
October-6
November-2
December-4
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YearCodesMemorizing Dates Continued 1900sadd1toyearcode
1800sadd3toyear
code
1700sand
2100s
add
5
toyearcode
2000+xx/4(ignoreremainder)
Add
new
number
to
xSubtractthenearestmultipleof7toreduce
(MonthCode+Date+YearCode)
nearestmultipleof7=
Day
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ArthurBenjamin
Mathemagician
http://www.math.hmc.edu/~benjamin/
http://www.youtube.com/watch?v=M4vqr3_ROIk
http://www.math.hmc.edu/~benjamin/http://www.youtube.com/watch?v=M4vqr3_ROIkhttp://www.youtube.com/watch?v=M4vqr3_ROIkhttp://www.math.hmc.edu/~benjamin/