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Maths KIRF

Key Instant Recall Facts

Multiplication Facts and Hints

 

Every multiplication has a twin, which may be easier to remember.

For example if you forget 8×5, you might remember 5×8. This way, you only have to remember half the table.

 

 

to multiply
by
Trick
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
when 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 = 10×66 = 60−6 = 54
 

when you add the answer's digits together, you get 9. 
Example: 9×5=45 and 4+5=9. (But not with 9×11=99)

 

When learning the 9 times table, remember that the number in the 10s column will be one less than the number they are multiplying 9 by.

For example, 8 x 9 will have a 7 in the tens column as it is 1 less than the 8 and the answer is a number bond to 9.  

Therefore 8 x 9 is 72 because 7 + 2 = 9.

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 when the sum of the digits is more than 9, we need to"carry the one". Example: 75x11 = 7(7+5)5 = 7(12)5 = 825.
12
is 10× plus 2×

 

 

Remembering Squares Can Help

This may not work for you, but it worked for me. I like remembering the squares (where you multiply a number by itself):

1×1=1 2×2=4 3×3=9 4×4=16 5×5=25 6×6=36
           
7×7=49 8×8=64 9×9=81 10×10=100 11×11=121 12×12=144

And this gives us one more trick. When the numbers we are multiplying are separated by 2 (example 7 and 5), then multiply the number in the middle by itself and subtract one. See this:

5×5 = 25 is just one bigger than 6×4 = 24
6×6 = 36 is just one bigger than 7×5 = 35
7×7 = 49 is just one bigger than 8×6 = 48
8×8 = 64 is just one bigger than 9×7 = 63
etc ...
 

 

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