Video Transcript
Subtraction of Numbers up to
100,000
In this video, we’re going to learn
how to use the most appropriate strategy to subtract numbers with up to five
digits.
These children are working on a
project about South American volcanoes. They’ve found out that the highest
active volcano on Earth is Ojos del Salado, which means salty eyes. It measures 22,615 feet. And the Sierra Nevada Mountain
range, which also lies in Argentina and Chile, measures 20,102 feet. They want to find the difference in
height between these two volcanoes, so they need to calculate 22,615 subtract
20,102. How could they calculate the
answer? Let’s take a closer look at how
they calculated their answers.
We could start with 22,615 and
subtract 20,000, which leaves us with 2,615. Then we could subtract 100 from
2,615, which would leave us with 2,515. There are no 10s in 20,102; we’ve
already subtracted the 1000s and the 100s. So, all that’s left is to subtract
the ones. 2,515 subtract two equals
2,513.
Another way to find the difference
would be to use column subtraction. Five ones take away two ones leaves
us with three ones. One 10 take away no 10s leaves us
with one 10. Six 100s take away 100 leaves us
with five 100s. There’s nothing to subtract from
our two 1000s, which leaves us with two 1000s. Now, we know that two take away two
is zero. So, there’s nothing left in the 10
thousands column. So, the difference between 22,615
and 20,102 is 2,513.
It doesn’t matter which strategy we
use to find the answer as long as we can work efficiently and accurately. And we can check if the answers are
accurate by adding together 20,102 and 2,513. We know that two plus three is
five. Zero 10s and one 10 gives us one
10. 100 and five 100s gives us six
100s. We’ve got two 1000s and two in the
10 thousands place 20,102 plus 2,513 is 22,615. We can check our subtraction
calculations using addition.
So, we’ve learned that we can use
any strategy to subtract and still reach the same result. And we can check our subtraction
calculations using addition. Let’s try some questions now where
we can think about the most appropriate strategy to use to subtract.
Complete the following: 87,652
subtract 1,550.
There are lots of strategies we
could use to calculate 87,652 take away 1,550. Let’s try to subtract mentally. We’re starting with 87,652, and
we’re going to subtract 1,550. We could start by subtracting the
1000 in 1,550. 1000 less than 87,000 is
86,000. The thousands digit has decreased
by one. 87,652 subtract 1,000 is
86,652. Next, we could subtract the
100s. The hundreds digit in 1,550 is a
five, which is worth 500. 86,652 subtract 500 is 86,152. Our hundreds digit has decreased by
five because we subtracted 500.
So, we subtracted the thousands,
the hundreds. Now, let’s subtract our tens. There are five 10s in 1,550. 86,152 subtract 50 is 86,102. Our tens digit has decreased by
five. We had five 10s. Now, we’ve got no 10s. We subtracted the thousands, the
hundreds, and the tens. And there are no ones in 1,550, so
we don’t have to subtract any ones. 87,652 take away 1,550 is
86,102.
81,252 take away 21,439 equals
what.
In this question, we have to choose
an appropriate way to calculate 81,252 subtract 21,439. These are both five-digit
numbers. It’s quite a tricky calculation to
do mentally, so we could subtract using the standard written method or column
subtraction. We’re starting with the number
81,252 which we’ve modeled using place value counters, and we need to subtract
21,439. So, let’s start by subtracting the
ones.
We’ve got two ones, and we need to
subtract nine. So, we’re going to need to
regroup. We need to take one of our 10s and
exchange it for 10 ones. Now, we’ve got 12 ones, and we can
subtract nine. We know that 12 take away nine is
three. Now, we can subtract in the tens
column. We’ve got four 10s, and we need to
take away three. Four 10s take away three 10s leaves
us with one 10. We’re going to need to regroup
again. We’ve only got two 100s, and we
need to subtract four. So, we can take one of our
thousands, which is our only 1000 and exchange it for 10 100s. Now, we’ve got 12 100s, and we can
subtract four. 12 take away four leaves us with
eight 100s.
We’re going to need to regroup
again. We’ve got no 1000s, and we need to
take away one. So, we can take one of our 10 1000s
and exchange it for 10 1000s. Now, we’ve got 10 1000s. We can subtract our one. And we know that 10 take away one
is nine. Now, what we need to do is subtract
in the 10 thousands column. We’ve got seven 10 thousands left,
and we need to subtract two. We know that seven take away two is
five. So, 81,252 subtract 21,439 equals
59,813.
Because we were subtracting a
five-digit number from a five-digit number, we decided to use the standard written
method or column subtraction. And we had to do quite a lot of
regrouping. So, we used the place value table
and counters to help us keep track. 81,252 take away 21,439 equals
59,813.
35,736 subtract 35,000 equals
what.
This is quite an easy subtraction
to work out mentally. The number we’re subtracting from
is 35,736. We could break this number apart
into an amount of thousands. And we know 35,736 has 35 1000s,
and the hundreds part of the number is 736. If we subtract 35,000, we’re just
left with 736. We used our knowledge of place
value to partition our number into an amount of thousands and hundreds. Then, we just subtracted our
35,000. 35,736 take away 35,000 equals
736.
What have we learned in this
video? We’ve learned that we can select
the most appropriate strategy to subtract. We’ve learned that sometimes a
mental strategy is the most appropriate to use, and sometimes it’s more efficient or
easier to use a written method.
