Rounding
To the nearest tens and to the nearest hundreds
What is rounding?
Rounding to the nearest tens or hundreds
place means finding the closest number
with no tens and no ones.
(Making it a "friendlier" number)
Examples:
678 can be rounded to 700
51 can be rounded to 50
Can you come up with a few examples?
Why do we round?
Sometimes, you do not need an exact
answer. You could be giving an estimate. In
that case, it makes it easier to round a
number to the nearest tens or hundreds
place.
Discuss opportunities that may require you
to estimate.
"Friendly" Numbers
Remember this problem?
28 + 56
We would rather answer 30 + 60 because
the numbers are friendlier.
Our answer is close, but not exact.
What makes them friendlier?
(They end in zero!)
Find the Friendly Numbers!
Which is friendlier, 0 or 10?
●
●
●
●
2
6
8
4
Partner Time
Using the number line, decide if 0 or 10 is
the friendly number for each number.
Create a T-Chart.
Find the Friendly Numbers!
Which is friendlier, 0, 10, or 20?
●
●
●
●
●
13
18
5
11
2
Find the Friendly Numbers!
Which is friendlier, 0, 10, or 20?
●
●
●
●
●
13
18
5
11
2
Rules for rounding
● If the number you are rounding is
followed by 5, 6, 7, 8, or 9, round the
number up.
○ Example: 38 rounded to the nearest ten is 40
● If the number you are rounding is
followed by 0, 1, 2, 3, or 4, round the
number down.
○ Example: 32 rounded to the nearest ten is 30.
Round to the nearest 10.
45
47
19
24
73
87
Round to the nearest 100.
532
945
894
396
The Rounding Rhyme
Find the digit,
Look next door
Five or higher,
Add one more
Four or less,
Let it rest!
Some Practice...
Round to the nearest 10:
72
Use the Rounding Rhyme!
"Find the digit..."
Round to the nearest 10:
72
tens
ones
"Look next door..."
Round to the nearest 10:
72
Five or higher? NO
Round to the nearest 10:
72
Four or less? Let it rest!
Round to the nearest 10:
72
70
Let's Try Again!
Some More Practice...
Round to the nearest 100:
586
Use the Rounding Rhyme!
"Find the digit..."
Round to the nearest 100:
586
hundreds
tens
ones
"Look next door..."
Round to the nearest 100:
586
Five or higher? ADD ONE MORE!
Round to the nearest 100:
586
Five or higher? ADD ONE MORE!
Round to the nearest 100:
586
600