First, read the English article below.

Round the number (to be added) up to the next highest multiple of ten. Add to the other number. Subtract the amount rounded up.  Example  88 + 56 = ? ; Round 88 up to 90.  Add 90 to 56 = 146  Subtract the two added to 88 (to round up to 90).  146 - 2 = 144 ; the answer! This process is simple reframing of the problem as 56 + (90 -2 ). Examples of other usages of this technique:  99 = (100 - 1); 68 = (70 - 2) You can use a similar reframing technique for subtraction, too. Multiplication is addition of multiple occurrences of the same number. Note how many times a number to be added is repeated. For example: 7 + 25 + 7 +7 +7 =  becomes 25 + (4 × 7) =  25 + 28 = 53 Additive opposites can be +7 - 7.  Additive opposites can also be 5 - 2 + 4 - 7. Look for numbers that add or subtract for a total of 0. Using the example above: (NOTE: The picture above is wrong. It shows 5 + 9 = 9 <--> -2 -7 = 9 when it should be 5 + 4 = 9 <--> -2 -7 = -9) 5 + 4 = 9 is the additive opposite of -2 -7 = -9 Since they are additive opposites, no actual addition of all four numbers is needed; the answer is 0 (zero) by cancelling. Try this:  4 + 5 - 7 + 8 - 3 + 6  - 9 + 2 =  becomes: (4  + 5) - 9 + ( -7 - 3) + (8 + 2) + 6 = By grouping  and remember, don't add them; just remove additive opposites from the problem.   0 + 0 + 6 = 6 

Now, please write a short abstract for it in Vietnamese. Abstract:
Quy đổi số cộng khó thành số cộng dễ. Quy đổi phép cộng thành phép nhân. Bỏ phép toán cộng đảo ngược (Additive Opposites).