The wonderful secrets of mathematics

An easy way to add two-digit numbers.

For example. 28 + 89 (80 + 9) =. We will write the 2nd addition in this view.
28 + 80 = 108
108 + 9 = 117

3. 
   Adding three-digit numbers.
   

For example. 728 + 347 (300 + 40 + 7) =
728 + 300 = 1028
1028 + 40 = 1068
1068 + 7 = 1075

4. 
   Method 2 for adding three-digit numbers.
   

For example. 878 + 797 (800-3) is just as easy to write.
878 + 800 = 1678
1678-3 = 1675

5. 
   Separate two-digit numbers.
   

For example. 79-46 (40 + 6) =
79-46 = 39-6 = 33

6. 
   Method for dividing two-digit numbers
   

For example. 85-39 (40-1) =
85-39 = 45-9 = 36 (the rule of subtracting 9 from 9, that is 45-9, we get 4 to 1 unit 5. 4-1 = 3, 5 + 1 = 6)

7. 
   A convenient way to divide three-digit numbers.
   

57 + 43 = 100
68 + 32 = 100
49 + 51 = 100
21 = 79 = 100
79 + 21 = 100
For example. 725-468 (write in 500-32.)
725-468 = 225 + 32 = 257
For example. 873-357 (write in 400-43.)
873-357 = 473 + 43 = 516
For example. 1428-571 (write 600-29.)
1428-571 = 828 + 29 = 857

8. 
   Multiply two-digit numbers by one-digit numbers.
   

42 (40 + 2) 7
40 7 = 280
2 7 = 14
280 + 14 = 294
Method 2:
69 (70-1) 6 =
70 6 = 420
1 6 = 6
420-6 = 414

9. 
   Multiply a three-digit number by a single-digit number.
   

326(300+20+6)
7
300 7= 2100
20 7= 140
6 7= 42
2282

10. 
    Calculate the square of numbers consisting of only 1 number.
    

There is a lot of trouble in solving such examples. There is a convenient way to do this.