Here is how I do column addition.
First 1 column at a time.
Next post I will do columns with 2 digits.
Let’s take Benjamins example:
In his example we see a matrix with 10 rows.
What I do is first add all numbers that add up to a round number (i.e. 10, 20, etc.).
Since we are doing right to left, let’s stick with that.
Most right column exist of the digits: 8 2 4 3 7 9 9 5 6.
In my mind I go over the digits and take out the digits that add up to 10 (or 20):
1: 8 2
2: 3 7 (skipping 4 for later)
3: 9 5 6 (while glancing over the digits I recognize 6+5 = 11. So almost immediately I see that the last 3 digits add up to 20).
My sub total is 40.
Left to do: 4 + 9 = 13
Total for first column is 53.
Write down 3 and carry 5.
The second column starts with 5, so take the carry and add the 5 to be the first 10:
1: 5 5
2: 6 4 (skip the 8 for the next step)
3: 8 2 (again we skip the 4)
4: 2 8
Sub total: 40
Left to do: 8 + 8 = 16
Total is 56. Write down 6. Carry 5.
Third row - including the carry - is: 5 9 8 8 …
It might not be immediately obvious that this adds up to a round number. However 5 + 9 = 14 and the complement of 8 is 2. Thus adding each 8 subtracts 2 from the last digit. So adding 2 8’s remove ‘4’ from the subtotal of 14.
In short 5+9+8+8 = 30.
Same with next 4: 8+7 = 15 and 6+9 = 15, so the next 4 digits add up to 30.
Subtotal for the first 7 digits is 60. left to do is adding ‘9+0+8’.
I hope you see immediately that this is 17.
Total is 77.
etc.
In short; I glance over the 10 digits in a column and remove the digits that add up to a round number.
I realize that this has a risk that you forget to add a digit.
However; for me, this goes pretty fast.
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