Multiplication with Number 11: Simple Warmup : Mental Math

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Simple Warmup

Mental math needs practice. Some will be compelling. But don't worry. It will be like learning to ride a bicycle. Once you grasp it, it will never leaves you!

Multiplication with Number 11

Whenever you multiply a number with 11, you can see a pattern in the product. Let's see it with an example.

Multiply 53 with 11

1. Write the unit digit of 53 (which is 3)
   3
2. Now add 3 with the next number (here 5) and write it to the left of the answer got on Step 1
   83
3. Add the left most digit (here 5) in front of
   583

Ta da!! Got it. 53 x 11 = 583

In other words, put a space between 53 and write the sum of them (5 + 3 = 8) between them. This is an easy way of thinking. But it will only work on 2 digits.

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Multiply 12 with 11

1. Write the unit digit of 12 (which is 2)
   2
2. Now add 2 with the next number (here 1) and write it in front  of the answer you got on Step 1
   32
3. Add the left most digit (here 1) in front of the answer.
   132


12 x 11 = 132

Multiply the following with 11

18

20

62

81

So what if the answer you get on Step 2 is a 2 digit number. Let's see with the following example.

Multiply 57 with 11

1. Write the unit digit of 57 (which is 7)
   7
2. Now add 7 with the next number (here 5) and write it in front  of the answer you got on Step 1. But you are getting 12 as the answer. So, write only the unit digit of 12 (which is 2) and keep the other (which is 1) in your mind.
   27
3. Normally you'll write 5 here. But in this case you have 1 in your mind. So add 1 and 5 and write 6.
   627


57 x 11 = 627 

Multiply the following with 11

64

99

83

91

What about more than 2 digit? We continue this process

Solve 532 x 11

1. Write the unit digit of 532 (which is 2)
   2
2. Add 3 and 2 and write it down.
   52
3. Add 3 and 5 and write it down 
   852
4. Now write 5 (as it is the left most number)
   5852


532 x 11 = 5852

Multiply the following numbers with 11

11

54

102

58

65

198

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