Warp Mass :: Multiplication Tricks Summary - (3)

I will cover the multiplication of ①two digits numbers, ②two digit number and three digit number, ③three digits numbers and ④four digits numbers.

The same trick will be applied to all of ①, ②, ③ and ④.

1. Calculation is handled from right to left.
   → 8 X 3
   → 8 X 5 + 4 X 3
   → 4 X 5
2. The number of sums increases one by one and then decreases one by one.
   → 8 X 3 - the number of sum = 1
   → 8 X 5 + 4 X 3 - the number of sum = 2
   → 4 X 5 - the number of sum = 1

• 48 X 53 = ?
          4  8
          |⤬|
     x   5  3
   ---------------
   20 | 52 | 24
   20 |   2 | 4
     5 |   2 |
   ---------------
    25    4    4
  
  

1. Calculation is handled from right to left.
   → 9 X 7
   → 8 X 7 + 9 X 9
   → 7 X 7 + 8 X 9 + 9 X 0
   → 7 X 9 + 8 X 0
   → 7 X 0
2. The number of sums increases one by one and then decreases one by one.
   → 9 X 7- the number of sum = 1
   → 8 X 7 + 9 X 9- the number of sum = 2
   → 7 X 7 + 8 X 9 + 9 X 0- the number of sum = 3
   → 7 X 9 + 8 X 0- the number of sum = 2
   → 7 X 0- the number of sum = 1

• 789 X 97
            7    8    9
            | ⤬ | ⤬ |
    x      0    9    7
   ---------------------------------
      0 | 63 | 121 | 137 | 63
   ---------------------------------
      6 |   3 |     1 |      7 |   3
      6 | 12 |   13 |      6
   ---------------------------------
      6 | 15 |   14 |    13 |   3
   ---------------------------------
      6 |   5 |   4 |    3 |  3
      1 |   1 |   1
   ---------------------------------
     7      6     5      3     3
  
  

Do Exercise

• 371 X 433
            3    7    1
            | ⤬ | ⤬ |
    x      4    3    3
   ---------------------------
   12 | 37 | 34 | 24 |  3
   ----------------------------
   12 |   7 |   4 |   4 |   3
     3 |   3 |   2
   ----------------------------
    16    0     6     4     3
  
  
• 1472 X 4215
                1     4     7     2
                 | ⤬ | ⤬ | ⤬ |
         x     4     2     1     5
   ---------------------------------------
    4 | 18 | 37 | 31 | 31 | 37 | 10
   ---------------------------------------
    4 |   8 |   7 |   1 |   1 |   7 |   0
    1 |   3 |   3 |   3 |   3 |   1
   ---------------------------------------
     6     2     0     4     4     8     0