SPECIAL MULTIPLICATION - Multiplication by 11

                                    Multiplication by 11 

Find 52 × 11. To multiply a 2-figure number, like 52, by 11 you write down the number being multiplied, and put the total of the figures between the two figures: 572.

 So 52 × 11 = 572, between the 5 and 2 we put 7, which is 5+2.  

  Practice A Multiply the following by 11: a 23 × 11   b 61 × 11   c 44 × 11   d 50 × 11    

                                        CARRIES 

Going back to multiplication by 11, there can sometimes be a carry, as the next example shows.

 Find 58 × 11. The 5 and 8 here add up to 13 so the 1 has to be carried to the left: 58 × 11 = 5138 = 638.

Find 47 × 11.  The 4 and 7 here add up to 11 so again you carry 1 to the left: 47 × 11 = 4117 = 517. 

Practice B Try these: a 68 × 11 b 79 × 11 c 47 × 11 d 86 × 11 e 55 × 11 f 93 × 11 

                                  LONGER NUMBERS 

This method can be easily extended to longer numbers.
Find 234 × 11. To multiply this 3-figure number by 11 you put the first and last figures of 234 as the first and last figures of the answer: 2 3 4 2 ? ? 4
Practice C Multiply the following by 11

 a 423 × 11 b 636 × 11 c 534 × 11 d 516 × 11 e 706 × 11 f 260 × 11 g 444 × 11 h 135 × 11 i 531 × 11 

When you add the first or last two figures you could get a 2-figure number, so that there is a carry figure.

 Find 777 × 11. The method above gives: 714147 = 8547. We simply carry the 1’s over, as before. 6 

Practice D  Multiply by 11:

 a 384 × 11 b 629 × 11 c 888 × 11 d 555 × 11 e 393 × 11 f 939 × 11