Video Transcript
Pick the sum equal to 3,324 plus
5,564. Is it 9,000 plus 800 plus 80 plus
eight, 8,000 plus 900 plus 80 plus eight, 8,000 plus 800 plus 80 plus nine, 8,000
plus 800 plus 80 plus eight, or 8,000 plus 800 plus 90 plus eight?
In this question, we’re given a
pair of four-digit numbers to add together. But instead of finding a number
that’s equal to their total, we’re asked to pick a sum. Our five possible answers are all
additions, and only one of them makes a total that’s exactly the same as the total
of the two numbers in the question. One way to find the answer could be
to start off by adding our two numbers together and then go through each of our five
possible answers adding them to see which one has the same total. But that’s a lot of addition we’d
need to do. And there’s a quicker way to find
the answer.
Can you spot anything interesting
about the five additions that are listed? Well, they each show a number of
thousands plus a number of hundreds plus a number of tens plus a number of ones. It’s almost as if our total of
3,324 and 5,564 has been split up into its thousands, hundreds, tens, and ones. Let’s try seeing how many
thousands, hundreds, tens, and ones there’ll be in our answer. Let’s break apart the two
four-digit numbers we’re given. Now, this is the sort of addition
we can do in our heads, but we’re going to make a note of everything that we do so
that it’s clear what strategies we’ve used.
So to begin with, let’s see how
many 1,000s there’re going to be in our answer. Our first number contains three
1,000s and there’s a five in the thousands place of our second number, and 3,000
plus 5,000 equals 8,000. Looks like the number of 1,000s in
our answer is going to be eight. And if we look at each of the
possible additions, we can see that one stands out. The first one has nine 1,000s, not
eight. So let’s cross this one
through. It’s not the right answer. The others though could be. Let’s break apart the hundreds. Our first number contains three
100s and our second number contains five 100s. This is a very similar addition to
the one we’ve just done, isn’t it? 300 plus 500 equals 800.
Now, if we look at our remaining
possible answers, we can see that most of them do have 800 as the hundreds number in
the addition. But can you spot one of them
doesn’t? The first one on our list has
900. So we’re gonna cross this
through. This one is not correct. Now it’s time to look at the
tens. Our first number contains two 10s
or 20 and our second number contains six 10s or 60, and 20 plus 60 equals 80. Now, if we look at our remaining
answers, we can see that two of them do have 80 in them. But if we look at the last answer,
we can see 8,000 plus 800 plus 90.
Let’s cross this one through. We want to be adding 80 not 90. Finally, we can break off the ones
in both of our numbers and add those. Four ones plus another four ones
makes a total of eight ones. We’ve found the total of 3,324 and
5,564 by breaking these two numbers apart, adding the thousands, then the hundreds,
then the tens, then the ones.
Now, if we were to find the actual
total, we’d combine all our answers together again. But of course, our question doesn’t
ask us to do this. We’re just looking for a sum that
represents 8,000 plus 800 plus 80 plus eight, and here it is. It would make an interesting
answer, wouldn’t it? 8,888. The sum that’s equal to 3,324 plus
5,564 is 8,000 plus 800 plus 80 plus eight.
