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Thursday, 14 November 2013
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Tricks by Number

2
add the number to itself (example 2×9 = 9+9)
5
the last digit goes 5, 0, 5, 0, ...
is always half of 10× (Example: 5x6 = half of 10x6 = half of 60 = 30)
is half the number times 10 (Example: 5x6 = 10x3 = 30)
6
if you multiply 6 by an even number, they both end in the same digit.
Example: 6×2=12, 6×4=24, 6×6=36, etc
9
the last digit goes 9,8,7,6, ...

your hands can help! Example: to multiply 9 by 8,
hold your 8th finger down, and count "7" and "2",
the answer is 72
  is 10× the number minus the number.
Example: 9×6 = 10×6 - 6 = 60-6 = 54
if you add the answer's digits together, you get 9.
Example: 9×5=45 and 4+5=9. (But not with 9×11=99)
10
put a zero after it
11
up to 9x11: just repeat the digit (Example: 4x11 = 44)
  for 10x11 to 18x11: write the sum of the digits between the digits
(Example: 15x11 = 1(1+5)5 = 165)

Note: this works for any two-digit number, but if the
sum of the digits is more than 9, you will have to
"carry the one" (Example: 75x11 = 7(7+5)5 = 7(12)5 = 825).
12
is 10× plus 2×
 
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