Transcript Round numbers to 1 significant figure.

Rounding and Estimating
Objective:
Round numbers to the nearest integer.
To round a number to the nearest integer (whole number), consider
its position on the number line:
Examples:
2
2.3
4.5
3
4
5.17
5
6
Find the nearest whole number value for each of the numbers:
2.3 is nearest to 2
4.5 is exactly halfway between 4 and 5 – in this case we
always round up, so the value we need is 5
5.17 is nearest to 5
A simple rule to find the nearest integer is to look at the first
digit after the decimal place. If this is a 0,1,2,3 or 4 then round
down, otherwise round up to the next whole number value.
Level 5
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Page 1
Rounding and Estimating
Objective:
Round numbers to a given power of 10.
75263
The number above shows how many people attended
a football match at the weekend.
To round this number to the nearest 10
You must first decide which options it lies between.
Think of the list of numbers either side of the number
you are rounding.
Now find the two numbers which you could be rounding
to in the list.
The number 75263 is closer to 75260.
Remember that if the number is exactly
halfway between then we always round up.
Level 5
© www.notjustsums.com
75259
75260
75261
75262
75263
75264
75265
75266
75267
75268
75269
75270
75271
75272
75273
Page 2
Rounding and Estimating
Objective:
Round numbers to a given power of 10.
75263
To the nearest 100: The number lies between 75200 and 75300
The important digit to consider is the tens digit
Because the tens digit is a 6, we round UP to 75300
To the nearest 1000: The number lies between 75000 and 76000
The important digit to consider is the hundreds digit
Because the hundreds digit is a 2, we round DOWN to 75000
To the nearest 10000: The number lies between 70000 and 80000
The important digit to consider is the thousands digit
Because the thousands digit is a 5, we round UP to 80000
Remember that if the number is exactly
halfway between then we always round up.
Level 5
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Page 3
Rounding and Estimating
Objective:
Round numbers to 1 significant figure.
Significant figures are any digits in a number except for zeroes on
the left hand side.
How many significant figures are there in each of the numbers
below?
57 2 significant figures
3 significant figures
All the digits are significant
108
except for zeroes on the left
hand side.
1 significant figure
0.7
5.02 3 significant figures
16089 5 significant figures
0.00503 3 significant figures
Level 5
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Page 4
Rounding and Estimating
Objective:
Round numbers to 1 significant figure.
To round the numbers to 1 significant figure, we look at the next
digit to see whether to round up or down.
0,1,2,3 or 4 tells us to round DOWN.
5,6,7,8 or 9 tells us to round UP.
57
The first significant figure is 5
The next digit is a 7 which tells us to round UP
57 to 1 significant figure is 60
0.042
The first significant figure is 4
The next digit is a 2 which tells us to round DOWN
0.042 to 1 significant figure is 0.04
Remember to keep the correct
place value of the digits.
Level 5
© www.notjustsums.com
Page 5
Rounding and Estimating
Objective:
Round numbers to 1 decimal place.
We can follow these steps when rounding to 1 decimal place:
• Find the first number after the decimal point.
• The next digit will tell us whether to round up or down.
0,1,2,3 or 4 tells us to round DOWN
5,6,7,8 or 9 tells us to round UP
Example:
6.792
The first decimal digit is 7
The next digit is a 9 which tells us to round UP
6.792 to 1 decimal place is 6.8
You can ignore any other digits later in the number.
Level 5
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Page 6
Objective:
Round numbers to 2 decimal places.
Rounding and Estimating
We can follow the same steps when rounding to 2 decimal places:
• Find the second number after the decimal point.
• The next digit will tell us whether to round up or down.
0,1,2,3 or 4 tells us to round DOWN
5,6,7,8 or 9 tells us to round UP
Example:
0.285
The second decimal digit is 8
The next digit is a 5 which tells us to round UP
0.295 to 2 decimal places is 0.29
Level 5
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Page 7