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Math tricks

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by

Leo Allen

on 26 June 2014

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Transcript of Math tricks

Odd
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
Full transcript