Additions Shortcuts

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

sponsored links

Read More...

Subtractions Shortcuts

PLEASE READ THE SHORTCUTS IN ADDITIONS FROM HERE FIRST. 

SO THAT IT WILL BE EASY FOR YOU TO UNDERSTAND SUBTRACTION SHORTCUTS 

SUBTRACTION BY NUMBERS CLOSE TO 100, 200, 300, 400, ETC.

250 - 96 

= 250 - (100 - 4) (here, instead of subtracting 96 from 250, we are just subtracting 100 from 250 and then adding 4) 
= 250 - 100 + 4 (Why adding? because the actual amount we have to subtract from 250 is 96. but we are subtracting 100. That means, we are subtracting 4 numbers more than we actually deserve. so our 250 will feel bad. so we should add that 4 to it:)

= 150 + 4

= 154

250 - 196

= 250 - (200 - 4) 

= 250 - 200 + 4 (here also same. In order to subtract 196, we subtract 200 and adding 4)

= 50 + 4

= 54

Note : We can use this logic for any number. According to our convenience.

Lets see, 

216 - 61 (Here i found it difficult to subtract 61 from 216)

= 216 - (100 - 39)  (So i just decided to subtract 100 to it and later will subtract the extra 39)

= 216 - 100 + 39 (Hey, see here. How about writing this 39 as 40 -1 ?)

= 116 + (40 - 1) (dont be confused. just practice this method and you will come to know how easy and efficient method it is :)

= 156 - 1

= 155

Subtraction of decimals

47 - 9.9 (How about dividing this 9.9 as 9 + 0.9 ??)

= 47 - (9 + 0.9)  we can write this as...

= 47 - 9 - 0.9  

= 38 - 0.9

= 37.1

18.3 - 0.8

= 18 + 0.3 - 0.8

= (18 - 0.8) + 0.3 

= 17.2 + 0.3 

= 17.5

sponsored links

Read More...