Video Transcript
Subtracting Hundreds from
Three-Digit Numbers
In this video, we will learn how to
use models to subtract a multiple of 100 from a three-digit number and investigate
which digits in the number change. In this video, we’re going to be
thinking about the value of digits. Before we learn how to subtract
from a three-digit number, let’s remind ourselves of the value of each of the
digits.
Three-digit numbers have a hundreds
digit, a tens digit, and a ones digit. Let’s make a three-digit number
using our digit cards. Our first digit is a seven. Let’s place it in the hundreds
column. Our next digit is a five. Let’s place it in the tens
column. And our third digit is an eight,
which we can place in the ones column. What number have we made?
Our first digit is a seven, and we
can see it’s in the hundreds column. The seven digit is worth seven
100s, and we’ve modeled this amount using seven 100s counters. So, the seven digit in our number
is worth 700. The tens digit in our number is a
five. We can model the value of this
digit using five 10s counters. So, the five digit in our number is
worth 50. Five 10s are 50. 10, 20, 30, 40, 50. Our ones digit is an eight. And this digit is worth eight
ones. So, the three-digit number we’ve
made is 758.
In this video, we’re going to be
subtracting hundreds from three-digit numbers and investigating which digits
change. What would happen to the number 758
if we were to subtract 100? If we take away one of our 100s
counters, instead of having seven 100s, we will only have six. 758 subtract 100 is 658. Did you notice which digit changed
in our three-digit number? It was the hundreds digit. When we subtracted 100 from 758,
the hundreds digit changed from seven to six. The hundreds digit decreased by
one; it went down by one.
Watch what happens to the hundreds
digit if we subtract 300 from 658. Our hundreds digit is a six, and we
have to subtract three 100s. Six 100s take away three 100s
leaves us with three 100s. 658 subtract 300 is 358. Did you notice what happened to the
hundreds digit? It decreased by three. Six 100s take away three 100s left
us with three 100s.
So, when we’re subtracting hundreds
from three-digit numbers, we only need to subtract in the hundreds column, and the
hundreds digit changes. Because we’re subtracting, this
digit will decrease. The number of hundreds will be
less.
Another model we can use to help us
subtract hundreds from three-digit numbers is a number line. If we want to subtract 200 from our
number 358, we could start at 358 and count back in hundreds. We’d need to make two jumps back of
100. Watch what happens to the digits in
our three-digit number as we subtract each 100. 358 subtract 100 is 258, and 258
subtract 100 is 158. Did you notice what happened to the
numbers as we subtracted 100 each time? The hundreds digit decreased by one
each time. Three, two, one.
What would happen if we were to
subtract 100 from 158? We’ve only got 100 left. If we take away our remaining 100,
we have no hundreds left. 158 subtract 100 is 58.
Let’s recap what we’ve learned so
far. We’ve learned that three-digit
numbers have a hundreds, tens, and ones digit. When we subtract a multiple of 100
from a three-digit number, we just need to subtract in the hundreds column. And the hundreds digit
decreases. Let’s practice what we’ve learned
now by answering some questions.
Fill in the blank. 675 take away 200 equals what.
In this question, we have to
subtract a multiple of 100, which is the number 200, from the number 675, which is a
three-digit number. Let’s model our three-digit number
using our place value table. 675 has six 100s, seven 10s, and
five ones. Let’s model our six 100s using six
100s counters.
Six digit is worth 600. The tens digit is a seven. And seven 10s are worth 70. And our five ones are worth
five. Now, we need to subtract 200. The ones digit in the number 200 is
a zero. So there’s nothing to subtract in
the ones. The tens digit is also a zero,
nothing to subtract from the tens. The number 200 has a two in the
hundreds place. So we need to subtract two 100s
from our six 100s. Six 100s take away two 100s leaves
us with four 100s. 675 subtract 200 equals 475. We found the answer using our
knowledge of place value.
Count back in hundreds to find the
difference. 429 subtract 300 equals what.
In this question, we have to
subtract 300 from 429. And the question tells us to use
the number line to count back in hundreds. So we need to start at the number
429, and we need to count back in hundreds three times because we’re subtracting
300. 100 less than 429 is 329. The hundreds digit has decreased by
one because we’ve taken away 100. 100 less than 329 is 229. So far, we’ve subtracted 200. Let’s subtract our final 100. 100 less than 229 is 129. 429 subtract 300 equals 129. We counted back in hundreds to find
the difference.
Find the difference by first
subtracting hundreds. 741 subtract 300 equals what.
In this question, we have to
subtract 300 from 741, and the question shows us a part–whole model. We’re told to subtract the
hundreds. So let’s break our number apart
into an amount of hundreds and the rest of the number. The number 741 has a seven digit in
the hundreds place, so the seven is worth 700. We’ve got four 10s, worth 40, and
one. 40 and one is 41. So, we’ve broken the number 741
apart into an amount of hundreds and its tens and ones. This makes it easy for us to
subtract the hundreds. 700 subtract 300 is 400.
Now we just need to put our number
back together again. Instead of having seven 100s, we’ve
got four 100s and 41. 400 plus 41 equals 441. To find the difference between 741
and 300, we just had to subtract an amount of hundreds. 741 has seven 100s. And we needed to subtract three
100s. So, the tens and ones digits didn’t
change, but the hundreds digit decreased from seven to four. 741 subtract 300 equals 441.
There are 342 boys and 200 girls in
a school. How many more boys than girls are
there in the school?
In this question, we have to find
the difference between the number of boys and girls in a school. To find the difference, we could
subtract the number of girls from the number of boys. We could subtract 200 from 342. The number 342 has three 100s, four
10s, and two ones. To subtract 200, all we need to do
is take away two of our 100s counters. Now we have 100 left, and our tens
and ones digits haven’t changed. Three 100s take away two 100s
leaves us with 100. 342 subtract 200 equals 142.
If there are 342 boys and 200 girls
in a school, then there are 142 more boys than girls. We calculated the answer using our
knowledge of place value.
What have we learned in this
video? We have learned how to subtract
hundreds from a three-digit number. We also learned that the tens and
ones digits stayed the same and the hundreds digit decreased.
