Play with 11 and find the answer in few seconds :-)

Multiplication with 11 is the most interesting thing and it can be done in 2 seconds. We all know the conventional method of Multiplication and that will take a minimum of 20 to 30 seconds in case of bigger numbers. With the following shortcut it is possible to reduce 80% of the time and any multiplication with 11 can be done in less than 10 seconds.

Example 1:

What is 35 x 11?

Step 1 – Keep the first digit and last digit as it is. 3__5.

Step 2 – add 3 and 5 (3 + 5 = 8). Write the Sum in between the above two numbers.

The Answer is 385.  

Example 2:

What is 45 x 11?

Step 1 – Keep 4 and 5 as it is. 4__5.

Step 2 – (4 + 5) = 9.

The Answer is 495. 

Example 3:

What is 34521 x 11?

Step 1 : Keep 3 and 1 as it is. 3______1.

Step 2 : Add the successive numbers from left side. (3 +4 = 7; 4 + 5 = 9; 5 + 2 = 7; 2 + 1 = 3).

The Answer is 379731

We can follow the above method only when the addition of numbers do not require any carry over. We cannot follow the same procedure for numbers with carry over. For eg consider 66 x 11. In this the sum of two numbers is more than 10 (ie 12). If we follow the same above method we will get the answer as 6126. But the correct answer is 726.

So there is another simple method called Star Method. In this method we add * at both ends and pro

Example 1: 

What is 66 x 11?

Step 1 : Adding stars at both ends. *66* (The value of * = 0)

Step 2: Add the numbers from right side. (* + 6 = 6; 6 + 6 = 12; 6 + * = 6).

Step 3: Write the sum in the reverse order. We get 6-12-6. Carry over the 1 in 12 to the left and add to it. So it becomes 7-2-6.

The Answer is 726.

Example 2:

What is 59 x 11?

Step 1: Adding Stars at both ends. *59*

Step 2: Adding numbers from right side. (* + 9 = 9; 9 + 5 = 14; 5 + *  = 5).

Step 3: Write the sum in reverse order. We get 5-14-9. Carry over the 1 in 14 to the left and add to it. So it becomes 6-4-9.

The Answer is 649.

Example 3:

What is 5684 x 11?

Step 1: *5684*

Step 2: (* + 4 = 4; 4 + 8 = 12; 8 + 6 = 14; 6 + 5 = 11; 5 + * = 5).

Step 3: 5-11-14-12-4. Start from right side and carry over the numbers to the immediate left in all. So we get 6-2-5-2-4.

The answer is 62524.

Example 4:

What is 39457 x 11?

Step 1: *39457*

Step 2: (* + 7 = 7; 7 + 5 = 12; 5 + 4 = 9; 4 + 9 = 13; 9 + 3 = 12; 3 + * = 3)

Step 3:  3-12-13-9-12-7. After carry over, we get 4-3-4-0-2-7.

The Answer is 434027.

Exercises:

1. 398 x 11    2. 3692 x 11    3. 21 x 11    4. 42 x 11    5. 97645 x 11