If the number is multiplied by 11 then the following procedure is to be followed to get the answer quickest.

Let’s understand these methods by taking an example.

345 × 11

Method 1:

Write 345 as 0345

Now multiply each and every digit by 1 and add it to its right neighbor.

Start from the right side.

Step 1:

Multiply 5 with 1 and add it to its right neighbor. 5 have no right neighbor so add the multiplication to 0. That is (5 × 1) +  0  = 5. This is right most digit of our answer.

0345 × 11 = xxx5
Step 2:

Multiply 4 with 1 and add it to its right neighbor 5. That is (4 × 1) + 5 = 9. This is second right digit of the answer.

0345 × 11 = xx95
Step 3:

Multiply 3 with 1 and add it to its right neighbor 4. That is (3 ×1) + 4 =7. This is third right digit of the answer.

0345 × 11 = x795

Step 4:

Multiply 0 with 1 and add it to its right neighbor. That is (0 × 1) + 3 = 3. This is leftmost digit of the answer.

0345 × 11 = 3795

So the answer is 3795.

You can notice that all these steps can be calculated mentally.

Method 2:

Write 11 as (10 + 1)

345 × (10 + 1)

= 345 × 10 + 345 × 1

= 3450 + 345

= 3795