Video Transcript
10 More and 10 Less: Numbers up to
100
In this video, we’re going to learn
how to find 10 more or 10 less than any number up to 100. And we’re also going to investigate
how the number of tens and the number of ones change.
Here’s 100 square. Each row of the 100 square contains
10 squares: 10, 20, 30, 40, and so on. Let’s stop at the number 40 for a
moment. How else could we show the number
40? We could use base 10 blocks. Four 10s and zero ones are 40. Now, how could we find 10 more than
40? We could put counters on another 10
squares. We’ve covered all the squares up to
50. 10 more than 40 is 50. To show 10 more using our base 10
equipment, we could add another 10s block. Instead of four 10s, we now have
five 10s. 10 more than 40 is 50.
Now, let’s find 10 less than
40. To find 10 less than 40, we need to
remove one lot of 10. So we could take away a row of
counters or one of our 10s blocks. Instead of four 10s, we now have
three 10s. And so, we can say 10 less than 40
is 30.
So far, all the numbers that we’ve
looked at have had zero ones. Let’s try working with a number
that does have some ones. This number has two 10s and five
ones; it’s the number 25. Now, what’s 10 more than 25? To find 10 more, we just need to
add one more 10s block. We did have two 10s. How many 10s do we have now? We have one lot of 10 more. So, we now have three 10s. And if we look at the number of
ones, it hasn’t changed; we still have five ones.
10 more than 25 is 35. Look how the number of tens has
gone from two 10s to three 10s. But the number of ones doesn’t
change at all. This is what happens when we find
10 more or 10 less. The number of tens changes, but the
number of ones stays the same.
Imagine you’ve made the number 83
out of these two-digit cards and you’ve been asked to show 10 less than 83. Which card would you change, the
orange one, the red one, both of them, or none of them?
As we’ve seen already, when we find
10 more or 10 less than a number, the tens digit changes, but the ones digit stays
the same. So we wouldn’t have to touch the
red card; we just swap the orange card to show 10 less than eight 10s. 10 less than 83 is 73.
Let’s have a go to answering some
questions now where we need to practice finding 10 more or 10 less than some numbers
up to 100.
Find 10 more than 20. Use the base 10 blocks to help
you. 20 plus 10 more equals what.
In this question, we’re starting
off with 20. And we can see this in the
picture. These blocks are 10s blocks; each
one is worth 10. And we can see two of them to start
off with, which is the same as 20. And our question asks us to find 10
more than 20. That’s why in the second part of
our picture we can see one more 10s block. This is the 10 that we need to add
to 20.
So, we’ve started off with two lots
of 10, and we’ve added one more lot of 10. How many tens should we have to end
with? Well, we know two plus one more is
three. Two 10s plus another 10 is going to
equal three 10s. And three 10s are worth 10, 20,
30. 20 plus 10 more equals 30.
Find the picture that shows 10 less
than 38.
To answer this question, we need to
choose one of the three pictures underneath. And in each of the pictures we have
a different number that’s been modeled using base 10 blocks. The yellow blocks represent tens
and the red blocks represent ones. To begin with, let’s try making 38
out of base 10 blocks. What would it look like? We could model the number 38 out of
three 10s and eight ones.
Now our question asks us to find a
picture that shows 10 less than 38. And in the number 38, as we’ve seen
already, it contains three 10s. If we want to find 10 less than 38,
how many tens is our new number going to have? Instead of three 10s, we’re going
to have to take away a 10. Instead of three 10s and eight
ones, our answer has two 10s and eight ones. The number of ones doesn’t change,
but the number of tens has.
Now we should be able to see
straightaway which one of our pictures shows the number 28. It’s the one made up of two 10s and
eight ones. This is the picture that shows 10
less than 38.
94 is 10 more than what.
This is a really interesting
question, because we might look at it quickly and think to ourselves, “I need to
find 10 more than 94.” But that’s not what the sentence
says. We could think of this sentence as
being a little bit like a number machine. We start off with a number that we
don’t know yet. We find 10 more. And then we get an answer of
94. Now, if we look at our picture at
the same time as reading the sentence, we might get an idea of how to work out the
answer. 94 is 10 more than what?
To find our missing number, we
don’t need to add 10 to 94. We need to work backwards through
our number machine. We need to find out what’s 10 less
than 94. To help us find 10 less than 94,
let’s use 10 frames. 94 is made up of nine 10s, which is
the same as nine full 10 frames, and then four ones. These are the four extra counters
on the end.
Now if we want to find 10 less than
94, what are we going to do? We can just take away one of our 10
frames. Instead of nine 10s, we now have
eight 10s. Notice how the ones digit hasn’t
changed though; we still have those four ones on the end. 10 less than 94 is 84.
Now, the way to find out whether
we’ve worked out the answer correctly is to put the number 84 in our original
sentence and see if it makes sense. 94 is 10 more than 84. Yes, that does make sense, doesn’t
it? It was a tricky question this one;
we had to work backwards to find the answer. The missing number is 84.
So, what have we learned in this
video? We’ve learned how to find 10 more
and 10 less than any number up to 100. We also know that the number of
tens changes, but the number of ones stays the same.
