Video Transcript
Jacob started training to join the
basketball team. In the first week, he scored a
total of 23 baskets. In the second week, he scored 12
more baskets than in the first week. Should I add or multiply to find
the number of baskets he scored in the second week? Why? Because “a total of” tells us to
use addition. Because “12 more” tells us to use
multiplication. Because “a total of” tells us to
use multiplication. Because “12 more” tells us to use
addition. Or because 12 more tells us to use
subtraction.
Questions like this are really
interesting because they’re not asking us to find the answer; they’re asking us how
we would find the answer. So we don’t have to work any
answers out to our calculation here. We just need to work out what the
calculation is. To begin with, let’s read that word
problem once again. And as we do, we could sketch a bar
model to help us understand what we need to do. So, firstly, we’re told that Jacob
started training to join the basketball team. In the first week, he scored a
total of 23 baskets. So we could draw a bar to represent
week one. And we’ll label it 23 to represent
all those baskets he scored in week one.
But it seems that Jacob’s training
pays off, doesn’t it, because we’re told that in week two, he scored 12 more baskets
than in the first week. How could we show the idea of 12
more than 23 on our bar model? Well, we could draw an extra bar
labeled 12. Those are the 12 more that he
scored. And then we could draw a new bar
that covers all of this length. And this is the number of baskets
that Jacob scores in the second week. Now, as we’ve said already, we’re
not asked to find out how many baskets Jacob scores in the second week. We’re just asked how we would do
this. Should we add or multiply? Well, we can see by looking at our
bar model, can’t we, that the length of the second bar is worth 23 plus 12 more. We’re going to need to add to find
the answer, aren’t we?
And then comes a really important
question: Why? How do we know that we need to add
and not multiply? What is it about the problem that
we were given that shows us that we need to add to find the answer. We’re given five possible
explanations here. Now perhaps the first time we read
through these, it might have sounded a little complicated, but we can get rid of
some of these answers straight away because we’ve already decided we need to add to
find the answer. We don’t need to use
multiplication, so we can cross through this sentence. And we know this sentence is wrong,
too. And we definitely don’t need to use
subtraction, do we? So we’re only left with two
possible answers.
And the only difference between
these answers are two little phrases. Did we see the words “a total of”
in the question and thought to ourselves, oh, we need to use addition? Or did we see the phrase “12 more”
and that’s what told us we needed to use addition? Well, firstly, we know that finding
the total of something does mean that we need to use addition. But when we go back to the question
and look at how those words are used, we’re just told in the first week he scored a
total of 23 baskets. In other words, this was the amount
he scored in week one. It’s got nothing to do with us
finding the answer to the question, has it? It’s just saying that was the whole
amount.
Now, if we find the phrase “12
more,” we can see that this is all about comparing the two weeks together, isn’t
it? In week two, he scored 12 more than
in the first week. This is where we find our answer,
and this is how we know we need to use addition. In this question, we didn’t solve a
word problem. We just thought about how we would
solve it. To begin with, we used a bar model
to work out that we needed to add to find the number of baskets that Jacob scored in
the second week. And we know we need to add because
“12 more” tells us to use addition.
