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Rounding Numbers

1.1 Number HOME | Achievement Criteria | BEDMAS | Rounding & Significant Figures | Sensible Rounding | Standard Form | Integers | Fractions With Calc | Fractions No calc | Fraction Applications | Recurring Decimals | Percentages of | % Increase & Decrease | % Applications | Interest & GST | Ratio | Ratio Changes | Proportion | Rates | Powers, Roots, Reciprocal | Compound Interest | Revision

2

Rounding & Significant Figures

What are Significant Figures?
Rounding numbers to decimal places (d.p.) and to Significant Figures (s.f.)

Khan Video Tutorial: Rounding | Sig Fig 1 | | Sig Fig 2 | Sig Fig 3 | Sig Fig 3

Activity
Round to 1DP | Significant figures (www.transum.org)

Class notes, pdf

p196 Ex 16.01
p14, Ex 1.06

NuLake p3,4,5

 

 

There are two ways to Round a number to a sensible answer
Rounding to Decimal Places (dp)
Rounding to Significant Figures (sf)
Count decimal places right from the decimal point
Count Significant figures from the first digit in the number (unless placehoder zeros)
8.245 has 3dp
8.245 has 4sf
15.2479 has 4dp
15.2479 has 6sf
400 has 0 dp
400 has 1sf
34 000 has 0dp
34 000 has 2sf
0.0023 has 4dp
0.0023 has 2sf
120.00459 has 5dp
120.00459 has 8sf
= 42.0 has 1dp
= 42.0 has 3sf (0 shouldn't be there so it must be important)

Mouse over above to find the dp. or sig figs.

Link to measurement page on rounding

 

When rounding cut the number at the required place & use the next digit to round.

0,1,2,3,4 stays the same. 5,6,7,8,9 rounds up by 1
   
Round 1.242826 to 2dp
Round 1.242826 to 2sf
1.24|2826    cut number at 2dp
1.2|42826    cut number at 2sf
1.24|2     Use the next digit to round
1.2|4    Use the next digit to round
1.24|      2 rounds down so leave the 4
1.2|4     4 rounds down so leave the 2
= 1.24 (2dp)
= 1.2 (2sf)

 

 

 

 
Round 0.03845 to 2dp
Round 0.03845 to 2sf
0.03|845    cut number at 2dp
0.038|45    cut number at 2sf
0.03|8     Use the next digit to round
0.038|4    Use the next digit to round
0.03|      8 rounds up so round the 3 up
0.038|    4 rounds down so leave the 8
= 0.04 (2dp)
= 0.038 (2sf)
 
 
 
 
Round 1289.98 to 1dp
Round 1289.98 to 2sf
1289.9|8    cut number at 2dp
12|89.98    cut number at 2sf
1289.9|8     Use the next digit to round
12|89.98    Use the next digit to round
1289.9|   8 rounds up so round the 9 up
12|00     4 rounds down so leave the 8
= 1290.0 (1dp)
= 1200 (2sf) Extra place holders are needed

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Round the following numbers?: (mouse over for answers)
1.26845 to 2dp = 1.27
1.26845 to 2sf = 1.3
0.0382468 to 3dp = 0.038
0.0382468 to 3sf = 0.0382
35.035823 to 2dp = 35.04
35.035823 to 2sf = 35
0.0892 to 2dp = 0.09
128458 to 2sf = 120000
0.0154 to 1dp = 0.0
9845 to 1sf = 10000

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