How to calculate the number easily, fastly

• Plus

 

12345+1000-2

=13345-2

=13343

 

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• Minus

 

1003-998

=(1000+3)-(1000-2)

=3+2

=5

 

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• Square

 

998^=?

(998+2)*(998-2)

(1000*996)+4=996004

 

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251^2+?=252^2

251-->252 : 251+251+1

=250+250+3=503

 

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15^2+?=16^2

15-->16 : 15+15+1

=31

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• The change in volume in a triangular pyramid if a radius is 98

 

For example,

- The area of a circle with a radius of 98

- The area of a circle : πr^2 --> π98^2

 

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• Geometric progression

 

Example 1.

 

1 + 2 + 4 + 8 = ?

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- Find the rule(pattern)

 

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- Blue - Black = Black

 

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- Move all the bars to the right side.

 

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the number that comes after the last number - first number

 

∴

 

1 + 2 + 4 + 8 = 16 - 1 = 15

 

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Example 2.

 

 

- Red - Black = Black * 2

- the number that comes after the last number :  (27 * 3) - 1

- ratio : pattern - 1 = 3 - 1

- Black : ((27 * 3) - 1) / ratio

 

https://youtu.be/FjPem4Jzses?si=qvAT1kEkqsj7FNUh

https://youtu.be/lkpqpFm9zcw?si=lTAc8M-ZOcWQ5ZqS

https://youtu.be/-x4DBQJXM94?si=qU_1DEeZ0pkQjosB