How to Subtract two two-digit numbers
Subtraction is not as hard as it might seem. When you have two different numbers to subtract, the easiest way is to make the numbers "similar" somehow. This means that we want to make one of the numbers(always the higher one) have the second digit equal to the smaller number. Let's do an example to see what I mean.
Examples
76 - 38 -> We want to make the second digit of the highest number to be the same as the second digit of the lowest
number. In other words for this example we want to change the 6 in 76 to an 8 so that both numbers end
with an 8. Remember always change the larger number only. Sometimes we might need change it by adding
to it and other times we might change it by subtracting.
Add 2 to 76 to make it 78. We now have:
78 - 38 = 40 (This is our intermediate answer)
Making the second digits in each number makes the subtraction easier because we can simply subtract
each number individually:
7 - 3 = 4
8 - 8 = 0
Remember My Little Rule in the addition section. Whatever you do at the beginning you must do the
equal and opposite at the end.
Since we added 2 to 76 at the beginning, we must subtract that same amount from the intermediate
answer to get the final answer.
40 - 2 = 38
73 - 42 -> When each digit of the second number is less than or equal to its corresponding digit in the first number
just subtract each of then individually. In our example the 4 in 42 is less than the 7 is 73 and the 2 is less
than the 3. We can just subtract from each one individually.
7 - 4 = 3
3 - 2 = 1
Therefore 73 - 42 = 31
We could also have done this example the way we did the first one above. We must change the higher
number so that its second digit is equal tothe second digit of the lower number.
Subtract 1 from 73 to get 72. We now have:
72 - 42 = 30
This time we subtracted 1 at the beginning so we must add 1 at the end to get the final answer:
30 + 1 = 31
81 - 47 -> Add 6 to 81 to make it 87. We now have:
87 - 47 = 40
Now subtract the 6 we added at the beginning
40 - 6 = 34
Therefore 81 - 47 = 34
63 - 21 -> Since each of the digits of the second number is less than the corresponding ones in the first number
we will subtract each digit individually
6 - 2 = 4
3 - 1 = 2
Therefore 63 - 21 = 42
