Transcript

INSTRUCTOR:

I'm going to work out 426 plus 378. First method I'm going to use will actually partition each number into its hundreds, tens, and units. So 426 is 400 and 20 and 6, and then 378 is 300 and 70, and 8.

And then if I combine the hundreds, that makes 700. If I combine the tens, that gives me 90. And if I combine the units, that's 6 plus 8, is 14. Then I simply add all of those up-- 790, 800, 804. So altogether, that comes to 804.

The other method would be to put 426 and 378 one underneath the other, using the column method. So if I write 426, 378 will go underneath like that so that the units are in the column, the tens are in a column, the hundreds are in a column. Add those up.

6 and 8 makes 14, so I write down the 4 and carry the 1. 2 and 7 makes 9, and then 1 makes 10, so I put down the 0 and carry the 1. 4 and 3 are 7, and 1 makes 8, so that's 804.

The column method is quicker, and may be more efficient. It relies on the digits being placed into columns-- the units in one column, the tens in another, the hundreds in another. And after we've lined up the digits, each of the numbers is added in their colours.

We're effectively treating each number as a string of digits, whereas in the first method, we're actually using the meaning of the 4 in 426 as 400, and the 2 meaning 20, and the 6 meaning six units-- and then similarly for the other number. But it is, obviously, a more chunky method, and not quite so quick to do. But they both come up with the same answer.