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.
- Calculation is handled from right to left.
→ 8 X 3
→ 8 X 5 + 4 X 3
→ 4 X 5 - 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
- 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 - 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