Multiplication Tricks

 Multiplication Tricks

Multiply by 2:   Add the number to itself

Anything multiplied by two must give an even number:

in other words, the last digit must be 2, 4, 6, 8 or 0.

Multiply by 3: It All Adds Up

Let's see if 3 has any special properties.

4 x 3 = 12     1 + 2 = 3

5 x 3 = 15     1 + 5 = 6

6 x 3 = 18     1 + 8 = 9

7 x 3 = 21     2 + 1 = 3

When you multiply by 3, the digits of the answer add up to 3, 6, or 9.

You can't really use this to multiply faster. But it is a quick way to check your work.

Multiply By 4

To quickly multiply by four, double the number and then double it again.

Show

             4

          x 3

           12

Cheer: 1, 2, 3, 4, all went marching out the door. (See 7 x 8)

4 x 4 = 16.  you must be 16 to drive a 4x4.

Multiply by 5: It's All 5s and 0s

Let's look at a few facts about 5.  If you multiply a number by 5 it must end in 5 or 0.

2 x 5 = 10

3 x 5 = 15

4 x 5 = 20

5 x 5 = 25

6 x 5 = 30

7 x 5 = 35

See a pattern? If we multiply by an even number, the ones digit is 0. If the number's odd, the ones digit is 5. This trick is great to check your multiplication by 5.

Multiply by 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

The rule doesn’t work for 6 times an odd number such as 6 x 3 = 18

Rhyme:  6 times 8 went on a date and didn’t come home ‘til they were 48.

              6 times 9 is 54—shut your mouth and say no more.

              6 x 6 is thirsty sixes

Multiply by 7:

Rhyme:

7x7 is San Francisco 49ers.

Five - six - seven - eight, Fifty-six is seven times eight.

Multiply by 8:

8 x 8 is Nintendo 64

Multiply by 9: It All Adds Up to 9

Have you ever heard of the Amazing Facts of Nine? Let's  take a look

.2 x 9 = 18   1 + 8 = 9

3 x 9 = 27    2 + 7 = 9

4 x 9 = 36    3 + 6 = 9

5 x 9 = 45    4 + 5 = 9

6 x 9 = 54    5 + 4 = 9

7 x 9 = 63     6 + 3 = 9

8 x 9 = 72     7 + 2 = 9

9 x 9 = 81     8 + 1 = 9

See the pattern? When we multiply a single-digit number times 9:

- The tens digit is one less than our original number.

- The tens digit plus the ones digit equals nine!

Multiply by 10: Just add 0

The easiest number to multiply by is 10. Just “add 0.”

3 x 10 = 30

140 x 10 = 1400

Multiply by 11:  up to 9x11:

 just repeat the digit (Example: 4x11 = 44)  

 for 10x11 to 18x11:  

 For this example we will use 11 x  54.

• Separate the two digits in you mind (5__4).
• Notice the hole between them!
• Add the 5 and the 4 together (5+4=9)
• Put the resulting 9 in the hole 594. That's it! 11 x 54=594

The only thing tricky to remember is that if the result of the addition is greater than 9, you only put the "ones" digit in the hole and carry the "tens" digit from the addition. For example 11 x 57 ... 5__7 ... 5+7=12 ... put the 2 in the hole and add the 1 from the 12 to the 5 in to get 6 for a result of 627 ... 11 x 57 = 627

Multiply by 12:

Multiply the number by 10 then by 2 and add them together.  For example  12 x 9 = ?

Multiply 9 by 10 = 90 and Multiply 9 by 2 = 18 then add 90 + 18 = 108 so 12 x 9 = 108