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Rounding & Significant Figures What are Significant Figures? Khan Video Tutorial: Rounding  Sig Fig 1   Sig Fig 2  Sig Fig 3  Sig Fig 3 Activity 
p196 Ex
16.01 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. 
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 
1.242826 cut number at 2dp 
1.242826 cut number at 2sf 
1.242 Use the next digit to round 
1.24 Use the next digit to round 
1.24 2 rounds down so leave the 4 
1.24 4 rounds down so leave the 2 
= 1.24 (2dp) 
= 1.2 (2sf) 


Round 0.03845 to 2dp 
Round 0.03845 to 2sf 
0.03845 cut number at 2dp 
0.03845 cut number at 2sf 
0.038 Use the next digit to round 
0.0384 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 
1289.98 cut number at 2dp 
1289.98 cut number at 2sf 
1289.98 Use the next digit to round 
1289.98 Use the next digit to round 
1289.9 8 rounds up so round the 9 up 
1200 4 rounds down so leave the 8 
= 1290.0 (1dp) 
= 1200 (2sf) Extra place holders are needed 
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 