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
