Add the digits.

If the sum is 0-9 put it between the 2 digits.

If it's 10-18 put the second number of the sum in between the digits, add 1 to the first digit.

Trick:

Example:

**11**

**10**

**5**

**multiply by:**

**multiple of:**

Divide by 2.

Take the smaller half

and put a 5 at the end.

Trick:

Example:

Even

1.

2.

1.

2.

Trick:

Example:

1.

Then add a 0 to the end

Divide by 2.

26

×5

______

17

×5

?

_____

Then add a 0 to the end

Divide by 2.

Even

?

26

×5

_______

130

17

×5

85

__________

11

×63

?

________

11

×63

693

_____________

11

×74

?

_____________

11

×74

814

______________

Add a 0 to the end.

It also works with 100. You just add two 0's. And with 1,000 you just add three 0's and so on.

57

×100

?

_______________________

84

×10

?

________________

84

×10

840

_____________

57

×100

5700

_________________________

**5**

**3**

**6**

Trick:

Example:

2.

1.

2.

Trick:

Example:

1.

2.

Trick:

Example:

1.

2.

If the number ends in a

5 or a 0 it is a multiple of 5

Is 57 a multiple of 5?

Is 7,845 a multiple of 5?

NO

57 is not a multiple of 5

YES

7,845 is a multiple of 5

It is a multiple of 3 if the digits add up to a multiple of 3.

This also works for 9's. It just has to add to 9.

Is 58 a multiple of 3?

NO

58 is not a multiple of 3

Is 4,284 a multiple of 3?

YES

4,284 is a multiple of 3

If a number is a multiple of 3 and a multiple of 2 [even] it is a multiple of 6

Is 582 a multiple of 6?

YES

582 is a multiple of 6

Is 423 a multiple of 6?

NO

423 is not a multiple of 6

Odd.

Divide by 2.

Take the smaller half and put a 5 at the end.

Is it a multiple of 9?

Yes

4,284 is a multiple of 9

**Math Tricks**