When subtracting two-digit numbers, your goal is to simplify the problem so that your problem turns to one digit subtraction or addition problem.
79 - 25
To solve 79 - 25, first, subtract 20 then subtract 5 (-25 = -20 - 5). After adding 30, you have a simple problem 59 - 5, which equals 54. We illustrate this as:
79 - 25
= 79 -20 -5
(first subtract 20)
= 59 - 5
(then subtract 5)
= 54
Subtraction problems are easily when there is not borrowing. To avoid this, we can change subtraction to addition. For instance, we have to subtract 72 - 39. Since it's borrowing. We can subtract 39 by subtracting 40, then adding 1. So, the question 72 - 39 = 72 - 40 +1 !
72 - 39
72 - 39
= 72 - 40 +1
(first subtract 40)
= 32 + 1
(then add 1)
= 33
Let's take another problem!
67 - 28
There are 2 ways to do it:
Solution 1:
67 - 28
= 67 - 20 - 8
(first subtract 20)
= 47 - 8
(then subtract 8)
= 39
Solution 2:
67 - 28
= 67 - 30 +2
(first subtract 20)
= 37 + 2
(then add 2)
= 39
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