Video Transcript
Find the missing three-digit
number.
To help us answer this question,
we’re shown a part–whole model. We’re given both parts, but we
don’t know the whole. And we’re told that this is a
missing three-digit number. But wait a moment! We know that it’s possible to have
a three-digit number without any tens, also without any ones, or even both. But it’s not possible to have a
three-digit number without any hundreds. And yet, if we look at the two
parts that make up our part–whole model, we can see that one of them represents a
number of tens and the other a number of ones. Where are the hundreds? What is this mystery three-digit
number?
Let’s try modeling our part–whole
model using a place value grid. Here are our five ones and 32
10s. But if we were to try writing this
using digits, we know that we could write a five in the ones place. But we also know we can’t write two
digits in the tens place. We’re going to need to regroup our
number. Although we can show this
three-digit number as 32 10s and five ones, if we want to write it using three
digits, we’re going to have to change some of our groups of tens. We know that 10 10s are the same as
one 100. And in the number 32 10s, we’ve got
three lots of 10 10s. And so we can exchange them for
three 100s. We can write our number as three
100s, two 10s, five ones.
We’ve used our knowledge of place
value here to exchange some of the many tens that we had for hundreds. 32 10s are the same as three 100s
and two 10s. And if we also include the five
ones, this makes our missing three-digit number 325.
