Multiplication Tips and Tricks

Some Tips and Tricks

Memory is your best friend! Having the whole table in your memory means no need to think, you just know that 3×15=15, 6×8=48 etc. Memory is fast, too.

Math Trainer - Multiplication is designed to help you remember your tables.

 

But here are some tricks that can help you doing multiplication.

Note: everyone thinks differently, so just ignore any tricks that don't make sense to you.

The Best Trick

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

For example if you forget 8×2, you might remember 2×8=16. This way, you only have to remember half the table.

multiplication table symmetry

Tricks by Number

2

add the number to itself (in other words, double it)
Example 2×9 = 9+9 = 18

4

double, then double again
Example 4×9: double 9 is 18, double 18 is 36

5

the last digit goes 5, 0, 5, 0, ...

is half of (10 times the number)
Example: 5x6 = half of 10x6 = half of 60 = 30

is 10 times (half the number)
Example: 5×6 = 10×3 = 30

6

when you multiply 6 by an even number, they both end in the same digit.
Examples: 6×2=12, 6×4=24, 6×6=36, etc

7×8

Think "5,6,7,8": 56=7×8

8

Double, double, double!
Example: 8×6: double 6 is 12, double 12 is 24, double 24 is 48

9

is 10× the number minus the number.
Example: 9×6 = 10×66 = 60−6 = 54

the ones digit goes 9, 8, 7, 6, ...: 9, 18, 27, 36, 45, ...
  the tens digit goes  0, 1, 2, 3, ...: 9, 18, 27, 36, 45, ...

subtract one to get the tens digit, and the tens and ones digit together make 9
Example: 9×5: tens digit is 4, 4 and 5 make 9, so 45
Example: 9×8: tens digit is 7, 7 and 2 make 9, so 72

fingers multiply 9


your hands can help! Example: to multiply 9 by 8, hold your 8th finger down, and count "7" and "2", the answer is 72


10

put a zero after it
Example: 10×2 = 20

11

up to 11x9: just repeat the digit. Example: 11x4 = 44

for 11×10 to 11×18: write the sum of the digits between the digits
Example: 11×15 = 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: 11×75 = 7(7+5)5 = 7(12)5 = 825.

12

is 10× plus 2×
Example: 12×4 = 40+8 = 48

15

multiply by 10, then add half again
Example: 15×4 = 40+20 = 60
Example: 15×9 = 90+45 = 135

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 ...