Additions Shortcuts

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Addition of numbers close to multiples of ten (e.g. 19, 29, 38, 59 etc.)

This technique is useful for Mental calculations

116 + 39 (Here we can write this 39 as 40-1)

= 116 + (40 - 1)

= 116 + 40 - 1

= 156 - 1 (Instead of adding 39 to 116, we just add 40 to 116 (because we can do this without using pen and paper) and later we subtract one from it)

= 155

Try this.. This is very useful tip while doing calculations.

Now lets try another example. 

116 + 97

= 116 + (100 - 3)

= 116 + 100 - 3  (Here, instead of adding 97 to 116, we are just adding a 100 to 116 and then subtracting 3 from it :)

= 216 - 3

= 213

Addition of decimals
12.5 + 6.25
= (12 + 0.5) + (6 + 0.25) 
= 12 + 6 + 0.5 + 0.25 (Here we just added the rounded numbers first and later we added the decimal numbers :)
= 18 + 0.5 + 0.25
= 18.75

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