Video Transcript
Rounding to the Nearest Ten
In this video, we will learn how to
round two-digit numbers to the nearest ten.
Here are some basketball shirts
drying on a line. The first shirt on the line is the
number 20, and the last shirt is number 30. We have to place shirt number 25,
28, and 23 in the correct place on the line. These three numbers all come
between the numbers 20 and 30. Where should we put the shirt with
the number 25? 25 is halfway between 20 and
30. Now, we’ve placed the number 25 on
the line. Where should we place shirt number
28? To help us compare these two
numbers, we need to look at each of the digits. Both numbers have two tens. 25 has five ones, and 28 has eight
ones. We know that eight is more than
five, so 28 is more than 25. So, we know that 28 comes after 25
on our line.
Where should we place number
23? 25 and 23 both have two tens. So, we need to compare the ones
digits. We know that three is less than
five and more than zero. So, 23 comes between the numbers 25
and 20, or we could say between the numbers 20 and 25. 23 should go about here on the
line. To help us place the shirts in the
correct place on the line, first, we thought about which two tens the number is
between. Then, we found the halfway point,
which was the number 25. Is number 23 nearest to 20 or
30? In other words, we need to round 23
to the nearest ten.
To do this, we need to look at the
ones digit. If the ones digit is less than
five, we have to round down. The ones digit in 23 is three, and
we know that three is less than five. So, the nearest ten to 23 is
20. If the ones digit is less than
five, we round down. So, what is the nearest ten to
28? The ones digit in the number 28 is
eight. If the ones digit is five or more,
we round up. Since we know that eight is more
than five, we need to round up to 30. The nearest ten to 28 is 30. What about the number 25? What’s the nearest ten to 25? We know if the ones digit is five
or more, we round up. So, the nearest ten to 25 is
30.
Let’s practice rounding two-digit
numbers to the nearest ten with some questions.
Round 46 to the nearest ten.
We’re shown a number line. The number line has been marked
with the number 46. We have to round the number 46 to
the nearest ten. 46 is between 40 and 50. Both of these numbers end in zero;
they’re both multiples of 10. Which is the nearest ten to 46? Is it 40 or 50? When we’re rounding numbers to the
nearest ten, we need to look carefully at the ones digit. If the ones digit is less than
five, we have to round down. If the ones digit is five or more,
we have to round up. We know that six is more than five,
so we need to round up to 50. The nearest ten to 46 is 50.
Round 24 to the nearest ten.
24 is a two-digit number. It has two tens and four ones. Two tens are 20. So, we know the number 24 comes
after number 20. And the next 10 after 20 is 30. Now, we know the number 24 comes
between 20 and 30. Let’s start at 20 and count until
we reach 24. 20, 21, 22, 23, 24. And, of course, we know the number
that comes after 24 is 25. 25 is halfway between the numbers
20 and 30. When we’re rounding numbers, we
have to look closely at the ones digit. If the ones digit is less than
five, we have to round down. We know that four is less than
five, so we need to round down. The nearest ten to 24 is 20. 24 rounded to the nearest ten is
20.
Round 89 to the nearest ten.
89 is a two-digit number. The eight digit is worth eight 10s
or 80. So, the number 89 is more than
80. And the 10 which comes after 80 is
90. The number 89 is between the
numbers 80 and 90. When we round a two-digit number to
its nearest ten, we have to look at the ones digit. If the ones digit is less than
five, we have to round down. And if the ones digit is worth five
or more, we have to round up.
Let’s place number 89 on the number
line. 85, 86, 87, 88, 89. 89 has nine ones. As nine is greater than five, we
need to round up. The nearest ten to 89 is 90. We rounded 89 to the nearest
ten. 89 rounded to the nearest ten is
90.
Which of the following numbers will
give 30 when rounded to the nearest ten? 31, 10, 24, or 36.
We have to decide which of the four
numbers will round to 30 if we rounded to the nearest ten. Where would we place the number 31
on the number line? The three digit in 31 is worth
three 10s, which are 30. So, we know that 31 comes after 30
on the number line. The 10 which comes after 30 is
40. Number 31 comes between 30 and 40
on the number line. 35 is halfway between these two
10s. We could position number 31 about
here on the number line. We know when we’re rounding a
number to the nearest ten, we have to look at the ones digit. If the ones digit is less than
five, we round down.
The number 31 has one in the ones
place. And we know that one is less than
five, so we have to round down. 31 rounded to the nearest ten is
30. So, we know that number 31 will
round to 30 if we rounded to the nearest ten. The nearest ten to the number 10 is
10. The nearest ten to the number 24 is
20. Four is less than five, so we round
down to 20. And the number 36 has three tens
and six ones. So, we need to round up to the
nearest ten, which is 40. The number which will give 30 when
rounded to the nearest ten is the number 31.
What have we learned in this
video? We’ve learned how to round to the
nearest ten using a number line. We know that if the ones digit in a
two-digit number is five or more, we round up. And if the ones digit in a
two-digit number is less than five, we round down.
