Calculation methods for addition

Philip and Kim are in the kitchen baking. They have two trays with 8 cookies on each. How many cookies have they baked? 8 plus 8 equals 16. It is quite easy to count in your head.

Okay but what is 251 plus 342 then? Ehrrmm...251 plus 342 is .. ... it is? Oh! Is there any method that makes it easier to calculate?

One method of adding larger numbers is to break the numbers down into ones, tens, hundreds, and so on. You break these numbers down into different place values. Then you add each place value together separately. Hundreds with hundreds, tens with tens and ones with ones. First the hundreds.

200 plus 300 is 500. Then the tens. 50 plus 40 is 90. And the ones. One plus two makes three.

Then add the hundreds with the tens and the ones, which makes 593. This method is called decomposing numbers. Here are two other numbers to add: 450,5 plus 341,2. Hundreds, tens, ones and tenths are split up separately. Then each place value is added individually and.. ..then the answer is 791,7 Pause the video to calculate and see if this is correct.

There are more methods. Here are two other numbers to add: 287 plus 115. 287 is a little less than 300 and 115 is a little more than 100. If you want to round up 287 to the nearest hundred, 300, you have to add 13. Then you have to subtract the same amount, 13, from the second number.

115 minus 13 is 102. 300 plus 102 is easier to calculate than 287 plus 115, because not many different place values need to be added. 300 plus 100 is 400 and then you just need to add two. The answer is 402. This method is called balancing.

Sometimes this third method works well. Try adding 468 and 324. First use the method decomposing numbers: Break them up into hundreds, tens, and ones. 400 plus 300 is 700. 60 plus 20 is 80 and 8 plus 4 is 12.

12 ones? That’s too many ‘ones’. Yes, when a digit gets bigger than nine, this method works: stacking. So how do we stack 468 plus 324? Write the ones in a column, tens in a column, and hundreds in a column.

And add the columns separately. Always start calculating from the right. Eight plus four is twelve. Twelve is written with the digits one and two. The ‘two’ digit is written in the ‘ones’ place value.

And the ‘one’ is carried over to the left and written above the ‘tens’ place value, to remind us to include it when counting the tens. Six plus two plus plus that one we carried over. That's nine. Now count the hundreds. Four plus three.

There is no number carried over this time so that makes seven. The answer is 792. When using stacking, if a number is greater than nine, carry the left digit over to the place value on the left. As happened when eight plus four made 12. These were three different methods for adding numbers: Decomposing numbers - adding numbers using place value Balancing numbers - to make them easier to add together.

Stacking - stack the numbers in columns. There are more methods. The most important thing is that you find a method that you understand, and want to use. Look Kim. I've stacked these cookies.

Now it will be easier to count them. Sorry, Philip!