Video Transcript
2,897 plus 5,497 equals what.
In this question, we need to find
the total of two four-digit numbers. Now, the way that this calculation
is being written, horizontally or across the page, might make us think that that’s
how we need to try to find the answer. We’ve just got to look at these two
four-digit numbers as they are and try to add them together. But never forget just because we’re
shown a calculation like this doesn’t mean we can’t rewrite it in a different
way. And when we’re adding two
four-digit numbers like this, a really helpful way to rewrite the calculation is
vertically, in other words, writing both numbers so that the thousands, the
hundreds, the tens, and the ones digits are on top of each other in separate
columns.
Now we can add each pair of digits
separately. And we always start by adding the
ones. Do you know why we always start by
adding the ones by the way? Before we begin, look at the two
digits in the thousands column and make a prediction. How many thousands do you think are
going to be in the answer? We’ve got 2,000 in our first number
and 5,000 in our second number. Well, we know two plus five equals
seven, so we might predict that our answer is going to contain 7,000. Well, we’d come back to that
prediction in a moment, but to begin with, let’s find the total of our ones.
Both numbers contain seven
ones. Seven plus seven equals 14
ones. Now we know we can’t show 14 ones
in the ones place because we can only show one digit. So we need to take 10 of our 14
ones and exchange them for one 10. We’ll write the little one
underneath like this. So we’re still showing 14 ones, but
we’re writing it as one 10 and four ones. If we look at our tens digits, we
can see that they’re both the same too. Both numbers have a nine in the
tens place. Nine plus nine is 18, so nine 10s
plus another nine 10s is 18 10s. We mustn’t forget the 10 that we
got when we exchanged either, so that’s 19 10s altogether. Again, this is a two-digit number,
so we’re going to need to exchange. We can take 10 of our 19 10s and
exchange them for one 100. So we can express 19 10s as one 100
and nine 10s.
In our hundreds column, we have
eight 100s plus another four 100s. This gives us a total of 12 100s,
but we can’t forget the one 100 that we’ve exchanged underneath. So that makes 13 100s. We’re going to need to exchange
again. A lot of exchanging in this
calculation, isn’t there? We need to take 10 of our 13 100s
and exchange them for one 1,000 because one 1,000 and three 100s is the same as 13
100s.
Finally, let’s add our two 1,000s
and five 1,000s that we talked about at the start. 2,000 plus 5,000 equals 7,000, but
we’ve got one extra 1,000 that we’ve exchanged. Instead of seven 1,000s, our answer
has eight 1,000s. Good job we didn’t start by adding
the thousands, isn’t it? This is why we always start on the
right and work to the left. It’s because if we have to regroup
in a column and exchange, the next column to the left is going to be affected. We found the total of these two
four-digit numbers by using the standard written method. 2,897 plus 5,497 equals 8,394.
