Making Your Math Simple Part II - Multiplication With 11 in Just 5 Seconds

Multiplying with 11

Multiplying by 11 is very easy and very interesting also.

For Example take 12345 x 11

Just forget about 11 and concentrate on 12345

Step 1 Take last digit of 12345 (i.e. 5) to the answer: Ans 5

Step 2 Add last digit of 12345 with immediate neighbor

i.e. 5+4=9

take it to answer Ans 95

Step 3 Add Next two neighbors of 12345

i.e 3+4=7

take it to answer

Ans 795

Step 4 Add Next two neighbors of 12345

i.e 2+3=5

take it to answer Ans 5795

Step 5 Add Next two neighbors of 12345

i.e 1+2=3

take it to answer

Ans 35795

Step 6 Take first digit of 12345 to answer :

Ans 135795

So Answer is 135795

Example:

120342 x 11

Lat digit taken to the answer 120342 Ans 2
Last digit added to neighbor 120342 Ans 62
Next two neighbors added 120342 Ans 762
Next two neighbors added 120342 Ans 3762
Next two neighbors added 120342 Ans 23762
Next two neighbors added 120342 Ans 323762
First digit taken to the answer 120342 Ans 1323762

So the Answer is 1323762

In case of carry, the carry is added to the total of neighbors

Example:

226987 x 11
Lat digit taken to the answer 226987 Ans 7
Last digit added to the neighbor 226987 Ans 57 ‘1’ carried over
Next two neighbors added + carry 226987 Ans 857 ‘1’ carried over
Next two neighbors added + carry 226987 Ans 6857 ‘1’ carried over
Next two neighbors added + carry 226987 Ans 96857
Next two neighbors added 226987 Ans 496857
First digit taken to answer 226987 Ans 2496857

Example :-

792421 x 11

Lat digit taken to the answer 792421 Ans 1
Last digit added to the neighbor 792421 Ans 31
Next two neighbors added 792421 Ans 631
Next two neighbors added 792421 Ans 6631
Next two neighbors added 792421 Ans 16631 ‘1’ is carried over
Next two neighbors added + carry 792421 Ans 716631 ‘1’ is carried over
First digit + carry taken to answer 792421 Ans 8716631

The problem can be solved in JUST one line

4526841 x 11

49795251

Try to apply the logic discussed in the previous examples and you will see that problem is solved in a single line.

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