Video Transcript
What is 336 subtract 45? Hint: Use place value blocks to
help you regroup.
In this problem, we’re asked to
subtract 45 from 336. And one of the useful ways that we
can subtract from a three-digit number like this is by setting out the calculation
as a column subtraction. This allows us to subtract the
ones, then the 10s, and the 100s separately. We’ve also been given a place value
grid here containing place value blocks. And they show our starting
number. 336 is made up of three 100s, three
10s, and six ones. Now we’re given a hint here. We’re told to use our place value
blocks to help us regroup. So let’s go through this column
subtraction step by step. And as soon as we need to use our
place value blocks, we will do so.
First, let’s subtract the ones. 336 contains six ones, and 45
contains five ones. And if we take away five ones from
six ones, we’re left with one one. That was simple enough. We didn’t need to use our place
value blocks, did we? Let’s take away five of our six
ones, though, just to show what we’ve done. There we go. We got one one left. Now it’s time to take away the
10s. 336 contains three 10s, and 45
contains four 10s. But wait a moment. The number of tens that we need to
subtract is greater than the number of 10s we have. Doesn’t look like we can do this,
does it? But when we stop and look at the
two numbers in this subtraction, we can see we definitely can take away four 10s
from 336. It’s just that we can’t subtract
them at the moment with the way that we’ve modeled this number.
This is where our hint comes in
handy. We’re going to need to regroup 336
so that we have enough tens. At the moment, we have three 100s,
so we can take one of those 100s. So instead of three 100s, we now
have two in the hundreds place. And we can write this digit two in
the box above. But we need to do something with
that 100 because we want the value to still be worth 336. So we’re going to have to exchange
that 100 for 10 10s. 10 10s are the same as 100. There we go. Now instead of three 10s, we’ve got
13 10s. And we’ll write this in the box
above too. Our hundreds digit has gone down
from three to two. So it might look like our number’s
become less.
But when we stop and read it, we
can see that it says two 100s, 13 10s, and six ones. And this is exactly the same as
336. It’s just been partitioned in a
different way, in a way that allows us to subtract those four 10s that we need to
take away. So let’s do that. 13 10s take away four 10s leaves us
with nine 10s. And now we don’t have any 100s to
take away, but we must remember we have two 100s and not three. So we still have two 100s. To help us subtract the number of
10s that we needed to, we regroup the number 336 to help us. 336 subtract 45 equals 291.
