Post on 23-Dec-2015
transcript
How do you ESTIMATE numbers?
Use the skill of ROUNDING
When do I use rounding?
• When the question asks you
to estimate.• When the question asks
“about how many”…?• When an exact answer isn’t
possible.• When an answer is difficult to obtain.
Try to Estimate the number of bricks used to
build this portion of a
chimney.
• 15 Bricks tall• About 4 bricks long• About 2 bricks wide
15 x 4 x 2 = 120 bricks
68,000
68,242
69,000
The population of the Sioux Reservation was 68,242. To the nearest thousand, what was the population?
68,242 is between 68,000 and 69,000, but it is closer to 68,000.
9
8
7
6
5 4
3
2
1
+0+1
Read this PoemFind your number.
Look right next door.4 or less just ignore.5 or more, add 1 more.
Now, Please take out your Math Notebook and write it down.
Round this number to the nearest
ten thousand.
Find your number.3 6 8,9 7
1Underline the number in the ten thousands place.
Round this number to the nearest
ten thousand.
Look right next door.
3 6 8,9 7 1
Circle the digit to the right of the underlined number.
Round this number to the nearest
ten thousand.
4 or less, just ignore.
3 6 8,9 7 1
8 is larger than 4 so go to the nextline of the poem.
Round this number to the nearest
ten thousand.
5 or more, add 1 more.
3 6 8,9 7 1Add 1 to the 6.
+1
Round this number to the nearest
ten thousand.
5 or more, add 1 more.
3 7 0,0 0 0Add 1 to the 6 and all the numbers
to the right of the 7 become 0’s.
The Answer
368,971 rounded to the nearest ten thousand is
3 7 0,0 0 0
Round this number to the nearest
thousand.
Find your number.
3 5, 3 2 7Underline the number in the thousands
place.
Round this number to the nearest
thousand.
Look right next door.
3 5, 3 2 7Circle to the right of the
underlined number.
Round this number to the nearest
thousand.
4 or less, just ignore.
3 5, 3 2 7
Since 3 is less than 4 we do not changethe 5.
Round this number to the nearest
thousand.
4 or less, just ignore.
3 5, 0 0 0
Change the numbers to left of 5 to 0’s.
The Answer
35,327 rounded to the nearest thousand is
3 5, 0 0 0
Round 73,852 to the nearest…
1. Ten-thousand.
2. Thousand.
3. Hundred.
4. Ten.
70,000
74,000
73,900
73,850
Round this number to the nearestdollar.
Find your number.
$ 5. 8 7
Underline the number where the dollars are.
Round this number to the nearestdollar.
Look right next door.
$ 5. 8 7
Circle to the right of the underlined number.
Round this number to the nearestdollar.
4 or less, just ignore.
$ 5. 8 78 is greater than 4 so go to the next
line of the poem.
Round this number to the nearestdollar.
5 or more, add 1 more.
$ 5. 8 7
Since 8 is greater than 5 add 1 to the 5.
+1
Round this number to the nearestdollar.
5 or more, add 1 more.
$ 6. 0 0Change the 5 to a 6 and change all the
numbers to the right to 0’s.
The Answer
$5.87 rounded to the
nearest dollar is
$ 6. 0 0
What about decimal numbers?
The same rules (and poem) apply!
Round 4.167 to the closest hundredths
4.167 Find your number
Look right next door
4.17
Special Case!Rounding a 9
Round 2.197 to the closes hundredths
Since there is a “9” in the hundredths place consider the tenth and hundredths together – 19 – do you leave it at 19 or move it to 20?
Round 4.95 to the closest tenth
Since there is a “9” in the tenth spot consider the ones and tenths
together…… should you leave it at 49 or move it to 50?
4.95 rounded to the nearest tenth is 5.0
Try these
Round to tenths:
4.56 4.6
5.32 5.3
0.98 1.0
Round to hundredths
18.784 18.78
9.456 9.46
9.997 10.00
Round this number to the nearest
tenth place.
Find your number.
4. 8 7 1Underline the number in
the tenths place.
Round this number to the nearest
tenth place.
Look right next door.
4. 8 7 1Circle to the right of the
Underlined number.
Round this number to the nearest
tenth place.
4 or less just ignore.
4. 8 7 18 is greater than 4 so go to the next
line of the poem.
Round this number to the nearest
tenth place.
5 or more, add 1 more.
4. 8 7 1Since 7 is greater than 5, add 1 to the
8.
+1
Round this number to the nearest
tenth place.
5 or more, add 1 more.
4. 9Change the 8 to a 9 and drop the
numbers to the right of the 9.
The Answer
4.871 rounded to the nearest tenth place is
4. 9
The End
Find your number.Look right next door.4 or less just ignore.
5 or more, add 1
more.
RememberIf you are asked to round to the nearest tenth…….your answer
stops at the tenth place!
Example: Round 42.73 to the closest tenth would be 42.7