Video Transcript
Column Subtraction of Three-Digit
Numbers: Subtracting across Zeros
In this video, we will learn how to
subtract from a three-digit number with zero 10s and record this calculation in
columns. Monster’s trying to subtract 125
from 509. Monster’s stuck. He started by subtracting in the
ones column. Nine take away five is four. Can you see what Monster’s problem
is? There are no tens in this
number. The monster has to subtract two
10s. Can you help him? What should he do? We can regroup. We can take one of our hundreds and
exchange it for 10 10s. 10 10s are 100. So now we have four 100s and 10
10s. Now Monster can subtract in the
tens column. 10 10s take away two 10s is eight
10s.
Now all we have to do is subtract
in the hundreds column. We had five 100s, but we had to
take one of our hundreds and exchange it for 10 10s. So now we have four 100s left. And we need to subtract one. Four subtract one is three. 509 subtract 125 is 384. Think Monster’s feeling much
happier now. Let’s remind ourselves of how we
helped Monster.
He managed to subtract five ones
from the nine ones. But when he got to the tens column,
he got stuck because the number 509 has no tens. And he needed to subtract two
10s. So we took one 100 and exchanged it
for 10 10s. Then, we were able to subtract in
the tens column. 10 take away two is eight. So to solve his problem, all
Monster had to do was regroup, exchanging 100 for 10 10s. We’re going to need to use our
knowledge of place value in this video. We’re going to use place value
counters or blocks to help us subtract. Let’s have a go at practicing what
we’ve learned now by answering some questions.
Solve the following: 402 subtract
34 equals what.
In this question, we have to
subtract 34 from 402 using the standard written method. Let’s model the number that we’re
subtracting from using some place value counters. The number 402 has four 100s, and
we’ve modeled this using four 100s counters. 402 doesn’t have any tens, so we
have no counters to place in the tens column. And we have a two digit in the ones
place, which we’ve modeled using two ones counters. Now we can start subtracting.
Remember, we always start in the
ones place: two subtract four. We have a bit of a problem. We don’t have enough ones. We’ve got two ones, and we need to
subtract four. Monster’s right; we need to
regroup. We could take one 10 and exchange
it for 10 ones. But wait! There are no tens to exchange. So we’re going to have to move to
the hundreds column. We need to take one of our hundreds
and exchange it for 10 10s.
Now we’ve got three 100s, 10 10s,
and two ones. But we still don’t have enough ones
to subtract four from. We need to regroup again. We need to take one of our
tens. Now we’ll have nine 10s left. And we need to exchange our 10 for
10 ones. Now we have 12 ones. Now we can start to subtract. 12 take away four is eight. Nine 10s subtract three 10s is six
10s. And there’s nothing to subtract
from our three 100s. 402 subtract 34 is 368. To find the answer, we had to
regroup twice. But we used our place value
counters to help. 402 subtract 34 is 368.
Subtract 335 from 401.
We can use the standard written
method to help us subtract. Let’s model the number we’re
subtracting from using place value counters. The number 401 has a four digit in
the hundreds place. We can model this with four 100s
counters. The tens digit is a zero, so we
don’t have to add any counters in the tens column. And the ones digit is a one, so we
just need to add a ones counter into the ones column. Let’s start by subtracting the
ones. One subtract five is what? Can you spot the problem? We don’t have enough ones to
subtract from. We’re going to need to regroup.
Normally, we would take a 10 and
exchange it for 10 ones. But there’s nothing in the tens
place, so we need to move into the hundreds column. We need to take one of our hundreds
and exchange it for 10 10s. Now we need to take one of our tens
and exchange it for 10 ones. Now we have 11 ones. We have enough ones to subtract our
five from. Let’s start subtracting now. 11 subtract five is six. Nine 10s subtract three 10s is also
six. And three 100s subtract three 100s
leaves us with no hundreds, but we don’t need to write this zero. 401 subtract 335 is 66.
Find the following: 800 take away
562.
In this question, we’re subtracting
a three-digit number from a three-digit number. And when we’re using the standard
written method, we always start by subtracting in the ones column. But we have a problem because 800
has no ones, and we need to subtract two. And we have another problem. There are no tens in the tens
column, so we need to move to the hundreds digit to help us regroup. We need to take one of our hundreds
and exchange it for 10 10s. And now we need to take one of our
tens and exchange it for 10 ones.
Now we can start to subtract in the
ones column. 10 take away two is eight. Next, we can subtract in the tens
column. We’ve got nine 10s, and we need to
take away six, which leaves us with three 10s. And finally, we can subtract the
hundreds. Seven 100s take away five 100s
leaves us with two 100s. 800 subtract 562 equals 238.
Find the following: 900 subtract
533 equals what.
In this question, we have to use
the standard written method to subtract 533 from 900. We could model 900 using our place
value chart. The only digit in 900 which has any
value is the hundreds digit. 900 has nine 100s, no tens, and no
ones. So before we can subtract in the
tens column and the ones column, we’re going to need to regroup. We can start by taking one of our
hundreds and exchanging it for 10 10s. But we still don’t have any ones to
subtract our three from. So we’re going to need to take one
of our tens and exchange it for 10 ones.
Now we have enough ones. Let’s start subtracting. 10 ones take away three ones leaves
us with seven ones. Nine 10s take away three 10s leaves
us with six 10s. And eight 100s take away five 100s
leaves us with three 100s. 900 subtract 533 is 367.
What have we learned in this
video? We have learned how to subtract
from a three-digit number with zero tens or ones by regrouping.
