Column Subtraction
Column subtraction is the opposite of column addition but is very similar. When we are subtracting numbers with more than 1 digit, we first organise the numbers into columns and subtract each individual column.
Then we subtract the numbers in the columns seperately, for example, here in the ones column we have 4 - 2 which is 2, so we write down 2 in the ones column, in the tens column we have 2 - 1 which is 1, so we write down 1 in the tens column, now we end up with 12. If there is a 0 in the first column (first as in going from left to right) then you can just leave that blank.
But sometimes this doesnt work, for example when I try and solve 26 - 17, the 2 numbers in the ones column, which are 6 and 7 which dont subtract as 6 is smaller than 7 meaning you can't subtract 7 from it, so how do I solve this? This is where we have to use borrowing. Lets use that example of 26 - 17, we allign the numbers into columns like last time, and in the ones column we now have 6 - 7, now we must borrow a ten from the 26 to change the 6 - 7 to a 16 - 7, where we can now solve it as 9 and put 9 as the answer for the ones column. However because we borrowed a 10 we need to take the 10 away from the 26, so we go to the tens column and subtract 1 from the 2, which gets us 1, so now we cross out the 2 and write in a 1 in it's place, then we can subtract the tens column to get 0, which leaves us with the 9 from the ones column.
So to review, when subtracting numbers with more than 1 digit, we organise them into columns based on digits and subtract the columns seperately, if the numbers in a column can't be subtracted because the top number is smaller than the bottom then we have to borrow an extra 1 from the column before (e.g in 26 - 17, in the ones column we have 6 - 7, we need to borrow a one from the column before, which is the tens column, so we borrow from 26)
Then we subtract the numbers in the columns seperately, for example, here in the ones column we have 4 - 2 which is 2, so we write down 2 in the ones column, in the tens column we have 2 - 1 which is 1, so we write down 1 in the tens column, now we end up with 12. If there is a 0 in the first column (first as in going from left to right) then you can just leave that blank.
But sometimes this doesnt work, for example when I try and solve 26 - 17, the 2 numbers in the ones column, which are 6 and 7 which dont subtract as 6 is smaller than 7 meaning you can't subtract 7 from it, so how do I solve this? This is where we have to use borrowing. Lets use that example of 26 - 17, we allign the numbers into columns like last time, and in the ones column we now have 6 - 7, now we must borrow a ten from the 26 to change the 6 - 7 to a 16 - 7, where we can now solve it as 9 and put 9 as the answer for the ones column. However because we borrowed a 10 we need to take the 10 away from the 26, so we go to the tens column and subtract 1 from the 2, which gets us 1, so now we cross out the 2 and write in a 1 in it's place, then we can subtract the tens column to get 0, which leaves us with the 9 from the ones column.
So to review, when subtracting numbers with more than 1 digit, we organise them into columns based on digits and subtract the columns seperately, if the numbers in a column can't be subtracted because the top number is smaller than the bottom then we have to borrow an extra 1 from the column before (e.g in 26 - 17, in the ones column we have 6 - 7, we need to borrow a one from the column before, which is the tens column, so we borrow from 26)
For example:
