Mental Subtraction

Here We see Mental Subtraction.

To Subtract Mentally, try and round off the number you are subtracting and then correct the answer.

(i.e) To subtract 9, take 10 and add 1; To subtract 8, take 10 and add 2; and so on.
For example, 47 – 9 = ?

The easiest and fastest method is to subtract 10, (37) and add 1 (38).
So the answer is 47 – 9 = 38.

To Subtract 27 from 44. Take 30, (14) and add 3, answer is 17.

Similarly to subtract a number near 100, take 100 and add the remainder.

• Subtracting One Number Below a Hundreds Value from Another which is just Above the same Hundreds Number.

This is easy method for mental subtraction. For example 124 – 86 = ?

Here 86 is 14 lower than 100, 124 is 24 higher than 100. So Add 14 to 24 for an easy answer of 38.

The Same principle applies for numbers above and below 10. For example, 15 – 6 = ?
(i.e.) 5 + 4 = 9 answer.

Similarly this works for any three digit subtraction.

For example, 445 – 286 = ?

286 is 14 lower than 300, 445 is 145 higher than 300. So the answer is 145 + 14 = 159.

Try these for yourself by applying the above method :-

39 – 7 = ?
54 – 38 = ?
436 – 84 = ?
134 – 76 = ?
152 – 88 = ?
14 – 9 = ?
834 – 275 = ?


Yes, Hope You have done all the above very easily and quickly.

MENTAL ADDITION

Addition is easier than Subtraction. Here we find a way how to make addition even easier.

We can easily add, 63 + 9 = 72, but how would you add this in your mind?

That is, to add 10 to any number, 16 + 10 is 26, 28 + 10 is 38, etc.,

In Mental addition, the basic is – To Add 9, Add 10 and Subtract 1; To Add 8, Add 10 and Subtract 2; To Add 7, Add 10 and Subtract 3; and so on.

Then, if you want to Add 49, Add 50 and Subtract 1; To Add 198, Add 200 and Subtract 2.
This makes it easy to hold numbers in your mind.

For example- 25 + 8 = ?; 33 + 7 = ?; 56 + 6 = ?;

Simple Principle for Mental Addition

If the units digit is high, round off to the next ten and then subtract the difference. If the units digit is low, add the tens, then the units.

For example,
47 + 26 = ?; 33 + 15 = ?; 95 + 38 = ?; 47 + 84 = ?; 56 + 75 = ?

We can use the same method for adding three digit numbers. You may prefer to add from left to right; adding hundreds, then the tens, and then the units.

Ex: 345 + 243 = ?; 586 + 654 = ?; 796 + 159 = ?;

In Adding larger numbers, When adding a column of numbers, add pairs of digits to make tens first then add other digits.

Ex: 1) 1236 + 1587 + 4598 = ? ; 2) 4587 + 8796 + 6879 = ?

Mental Addition is easier than the effort of finding a pen and paper or calculator.