Lets say you are to add 341+456, in this case the usual approach that we are taught in schools involves starting from the units digit and then proceeding to the left till the hundred’s place digit.

Accordingly to add 341 and 456, we first add 1 and 6, then 4 and 5 and then 3 and 4.

##### Drawback:

However this approach would not really help us in our day to day calculations as it does not favor mental addition mainly due to carries involved in between. In fact, the complexity increases when you are supposed to add more than two numbers.

So then, how do we add numbers mentally? Well, the solution is to add them from left to right. A left to right approach reduces the dependency on carry thus making it easier on your head to add numbers.

### Adding Two Digit Numbers from Left to Right:

In this section, you will learn an addition trick to add two digit numbers.

##### Approach:

Lets say you want to add 87 and 69, the steps involved in left to right approach:

1. First add the tens place digit in second number with the first number: 87 + 69 = 147
2. Then add the units place digit in second number with the result obtained in previous step: 147 + 9 = 156.

As you can see, you have added two numbers without the overhead of remembering the carry. This left to right approach also becomes easier when you are to add multiple numbers in your head.

### Adding Three Digit Numbers from Left to Right

Similarly to previous example, lets extend the addition trick to add three digit numbers from left to right.

##### Approach:

Lets say you want to add 953 and 867, the steps involved in left to right approach:

1. First add the hundreds place digit in second number with the first number: 953 + 800 = 1753
2. Then add the then place digit in second number with the result obtained in previous step: 1753 + 60 = 1813
3. Next add the units place digit in the second number with the result obtained in Step 2: 1813 + 7 = 1820

The above technique can be extended to n digit addition as well.

Now, lets consider a specific case of addition using subtraction trick. We can solve two digit addition problems by converting them into easy subtraction problems, when either of the numbers is close to the multiple of 10.

#### Example 1: 74 + 59

1. In 74 + 59, 59 is close to multiple of 10, hence it can be written as 60 – 1. Thus 74 + 59 = 74 + (60 – 1)
2. Now we simplify addition by first adding 60 with 74 => 60 + 74 = 134
3. And then subtracting 1 from the result obtained in previous step: 134 – 1 = 133

#### Example 2: 643 + 287

Similar to previous example, we can convert three digit addition problems into easy subtraction problems, when either of the numbers is close to the multiple of 100.

1. In 643 + 287, 287 is close to multiple of 300, hence it can be written as 300 – 13. Thus 643 + 287 = 643 + (300 – 13)
2. Now we simplify addition by first adding 643 with 300 => 643 + 300 = 943
3. And then subtracting 13 from the result obtained in previous step: 943 – 13 = 930