Fast Calculations In Mathematics: (Multiplication Module 1: Part a - Multiplication By 11)

 Multiplication Of Any Two-Digit Number (Let Say Ab) By 11:

 A) WHEN (A+B) IS BETWEEN 0 TO 9: A  (A+B)  B             

          EXAMPLES:  1)  11 X 42 =   4 ( 4+ 2) 2  =  462
                                2)  11 X 53 =   5 ( 5+3) 3   =  583
                                3)  11 X 12 =   1 (1+2) 2    =  132  
                                4)  11 X 23 =   2 (2+3) 3    =  253         

    B) WHEN (A+B) IS GREATER THAN 9: A  ( A+B)  B   
                                                                                ⇓
                                                                    CARRY OVER A
 

         Examples: 1) 11 X 57 = 5 (5+7) 7  ⇒ 5 (12) 7  ( Here carry 1 over 5) ⇒ (5+1) (2)  7  = 627
                          2) 11 X 93 = 9 ( 9+3) 3 ⇒ 9 (12) 3 ( Here carry 1 over 9) ⇒ (9+1) (2)  3 = 1023
                          3) 11 X 59 = 5 ( 5+9) 9 ⇒ 5 (14) 9 ( Here carry 1 over 5) ⇒ (5+1) (4) 9 = 649
                          4) 11 X 78 = 7 (7+8) 8  ⇒ 7 (15) 8 ( Here carry 1 over 7)⇒ (7+1) (5) 8 = 858

Problems: Find Out The Following Multiplications Mentally :

1) 11X27, 11X62, 11X71, 11X80, 11X33 , 11X45, 11X90, 11X10, 11X11, 11X42.

2) 11X58, 11X46, 11X79, 11X88, 11X65, 11X89, 11X77, 11X29, 11X56, 11X48.