2. Rounding means reducing the digits in a number whi le trying
to keep its value simi lar. The result is less accurate, but
easier to use.
There are 3 ways we can round numbers:
Using a number line:
Using place value
Using mental math
ROUNDING
3. USING A NUMBER LINE
Using a number l ine can be an easy method to round
numbers, but you need to be very careful and place the
numbers correctly.
Example: I want to round the number 134,456 to the nearest
hundred thousand. In order to do that I must first know where
the hundred thousand digit is. In this case, because I already
know place value, I know that the hundred thousand place is
the 1.
1 3 4 4 5 6
Hundred
thousands
Ten
thousands
Thousands Hundreds Tens Ones
4. USING A NUMBER LINE
I make a number l ine and place my number 134,456 between
100,000 and 200,000 thousand.
134,456
I can see that my number is closer to 100,000 than to
200,000 so:
134,456 rounded to the nearest hundred thousand = 100,000
5. USING PLACE VALUE
Number l ines can take a lot of time, especially if you need to
do a lot of exercises. A sometimes quicker way is using place
value.
Using this method, you need to fol low a couple of steps.
Before fol lowing them, though, you need to remember place
value in order to know the digit you are going to be rounding.
In this case, we want to round 134,456 to the nearest
hundred thousand, so we have to determine which digit is in
the hundred thousands place.
1 3 4 4 5 6
Hundred
thousands
Ten
thousands
Thousands Hundreds Tens Ones
6. Step One:
Look to the number of the right.
134,456 Since we are going to round the 1, we need to look at the
number on the right of it, which is the 3.
Step Two:
If it’s a number between 0 -4, the rounding number stays the same.
If it’s a number between 5 -9, add 1 to the rounding number.
3 is between 0-4, therefore, the rounding number (1) stays the same.
Step Three:
Replace the remaining numbers to the right of the rounding number with
zero.
100,000
USING PLACE VALUE
7. USING MENTAL MATH
This is perhaps the easiest way to round, but you must be very
careful when employing this method.
We fol low the fi rst few steps of the other methods:
Determine which digit we need to round.
Look to the digit on the right.
We are rounding 134,456 to the nearest hundred thousand. We
need to round the 1, and we look to the 3 for guidance.
If we use mental math, we know that the number 13 (we took the
two digi ts and made them a number) is closer to 10 than i t is to
20, therefore, the fi rst two digi ts remain as 10, and we simply
replace the other digi ts wi th zero.
134,456 to the nearest hundred thousand = 100,000.
8. MORE EXAMPLES
548,652 to the nearest TEN THOUSAND.
5 4 8 6 5 2
Hth Tth Th H T O
Number line:
Place Value:
548,652
Look to the right of the ten thousands place.
8 is between 5-9 so I add 1 to my rounding number (4+1 = 5).
Turn the remaining numbers to zero.
550,000
Mental Math:
Look to the right of the ten thousands place.
48 is closer to 50 than to 40, so I replace those two digits with 50.
Turn the remaining numbers to the right to zero.
550,00
9. PRACTICE!
Practice these exercises in your notebook, then look at the
Answer Key to see i f you got it right! You may use the method
that is easiest for you.
(1) 69,587 to the nearest HUNDRED
(2) 709,051 to the nearest HUNDRED THOUSAND
(3) 1,405 to the nearest TEN
(4) 33,985 to the nearest THOUSAND
(5) 95,201 to the nearest TEN THOUSAND
10. T h e se a r e t h e a nswe r s to t h e p r ev io us s l i d e’ s exe rci ses .
(1) 69,600
(2) 700,000
(3) 1,410
(4) 34,000
(5) 100,000
ANSWER KEY
11. CREDITS
Lesson prepared by: Mrs. Shiara Agosto
For: 4th grade class, C.E.T. Colegio Myrang, Carol ina, Puer to Rico
Common Core Standards: CC.4.NBT.3 Use place value
understanding to round multi -digit whole numbers to any place.
DISCLAIMER: You may distribute, copy, and/or alter the
contents of this lesson for personal or classroom use, as long
as you leave this sl ide intact and give credit where credit is due.
Thank you.
