Over the past few weeks we have been learning to use the Column Method to solve addition and subtraction problems. We started off adding and subtracting 2 digit numbers and ended up subtracting 3 digit numbers from 3 digit numbers.
The first thing we learned was that we need to make sure that each digit in each number is lined up correctly; the ones underneath the ones, the tens under the tens and the hundreds under the hundreds. When subtracting, the bigger number must always be on top. Next we start adding or subtracting from the ones column and it is always from top to bottom. When we add sometimes the numbers will add up to 10 or more which means we need to carry over either a ten or a hundred. As some of us learned it's easy to forget to add your extra ten or hundred so we made sure we wrote it below the answer lines. When it comes to subtracting sometimes the top number is smaller than the bottom number for example 3 - 8. If you have 3 sweets you cannot give someone 8. When this happens you need to go next door to your neighbour the tens or the hundreds and exchange one of them for a ten or a hundred. Don’t forget to cross one of them off and then add it to the column where the number was not enough. Now you should have enough to perform your subtraction.
Once we had mastered the technique we were able to add and subtract 3 digit numbers to and from each other confidently crossing the tens and the hundreds. Wow! How cool is maths?