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Multiplication by 12

To multiply a number by 12, follow these steps:

  • Multiply the last digit by 2. Write down the last digit of this product and carry if necessary.
  • Move to the next digit to the left.
  • Multiply that digit by 2 and then add that product to the digit on its right. Finally, add the carry from the previous steps. Write down the last digit and carry if necessary.
  • Continue to move to the left, multiply by 2, add to the right, write and carry until you reach the end of the number.
  • At the end, you will have to multiply the leading 0 by 2 and then add to the right.

 

Example:

31 × 12 =

Multiply 1 by 2. 1 × 2 = 2. 2
Move to the left and to the 3.  
Multiply 3 by 2, and then add 1 (the number on the right).  
(3 × 2) + 1 = 6 + 1 = 7. 72
Move to the left again, but since there is no more numbers, you use 0.  
Multiply 0 by 2, and then add 3 (the number on the right).  
(0 × 2) + 3 = 0 + 3 = 3 372

31 × 12 = 372.

 

Example:

917 × 12 =

Multiply 7 by 2. 7 × 2 = 14. Write 4, carry 1. 4 (carry 1)
Move to the left and to the 1.    
Multiply 1 by 2, and then add 7 and add the carry.    
(1 × 2) + 7 + 1 = 10.    
Write 0, carry 1. 04 (carry 1)
Move to the left and to the 9.    
Multiply 9 by 2, and then add 1 and then add the carry.    
(9 × 2) + 1 + 1 = 20    
Write 0, carry 2. 004 (carry 2)
Move to the left and to the invisible 0.    
Multiply 0 by 2, add 9 and add the carry. 9 + 2 = 11.    
Since this is the last number, write the whole number down. 11004  

917 × 12 = 11004.

 
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