Special Cases of Multiplication II

Multiplication by 11

a) Multiplication by 11 of any two digit number, whose sum of the digits is less than 10

i) 63 x 11 = 693

In such multiplication we do not carry out any multiplication but simly put the sum of the digits of multiplicand between it digits.

Hence, the unit’s place digit is 3  and ten’s place digit is 6  we put 9 ( 6 + 3 ) in between 6 and 3 to get 693

ii) 72 x 11 = 7 (ten’s place digit) 9 ( 7 + 2 ) 2 (ten’s place digit) = 792

b) Multiplication by 11 of any two

digit number, total of whose digits is

more than 10.

If the sum of the digits of multiplicand is more than 10 then put unit’s place digit of multiplicand as unit’s place digit of product and add the ten’s place dgit to the multiplicand and put this sum to the left of unit’s place digit of the multiplicand to get the final product.

i) 89 x 11 =

The sum of 8 and 9 is 17 so write 7 next to unit’s place digit i.e 9. latter carry on 1 and add it to the ten’s place digit i.e 8 + 1 = 9, put it next to 7.

89 x 11 = 979

ii) 78 x 11 = (7 + 1) 1 is carried on after adding 7 + 8 = 15 / 5 ( 7 + 8 = 15) / 9 ( units place digit.