11 * Any 2-Digit Number (Part 1)


Rule 1.0

The product of 11 and any 2-digit number (AB) begins and ends with the two digits of the multiplier; the number in the middle is the sum of the original two digits


Equation 1.0

11 * _ _ = _ _ _ 

11 * AB = A(A+B)B

Example: 11 * 23 = 2(2+3)3 = 253


Practice 1.0

 

 

 


Rule 2.0 (Exception)

For a multiplier whose digits sum to a number greater than 9, you have to carry.

Example: 11 * 85 = 

AB = 85

A+B > 9?

yes

8+5 = 13 > 9

A+B = CD > 9

(A+C)DB

(8+1)35 = 935