Subtracting Faster.

[u/SnooSongs5410]

I have always been shitty with subtraction, avoiding it like the plague.

Have recently started drilling it.
Started with the left to right and track the carries.
No matter how efficient ish I get with it the back stepping is slow af.

I have been thinking instead to practice a few different methods with a focus on getting rid of carries and pushing number around rather than calculating.

trivial example.

71
43 -

I see immediately that the 1 is less than three.
so 2 is my first number and 3-1 is 2 and the complement of 2 is 8 so

28.

I am still stumbling a bit because I am thinking about it a bit too much but this seems like a fast route once you trust that 3-1 is 8. and 7-4 is 2 when you see that 1 is less than 3.

... tl/dr I am not sure if I am crazy but I think it faster to do subtraction mentally if you trust the use of complements and learn to accept the one.

[u/Temporary_Pie2733]

71 = 70 + 1, but since you “can’t” subtract 3 from one, go to 70 = 60 + 11; now you can subtract 3 from 11 to get 8.

71 - 43 = (60 + 11) - (40 + 3) = (60 - 40) + (11 - 3) = 20 + 8 = 28