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A4. Real numbers : significant figures. In any decimal number, the first non-zero number in it is called the first significant figure. The digit shown in red in these numbers is the first significant figure: 6789 12.013 0.0456 30.01 199 822.0009 0.0005 404 4.00008 333 72 0.00108 The digit that follows the first significant figure in a number (whether or not it is zero) is called the second significant figure. The digit shown in green in these numbers is the second significant figure: 6789 12.013 0.0456 30.01 199 822.0009 0.0005 404 4.00008 333 72 0.00108 In a similar way we can identify the third significant figure, and fourth, and so on. Approximate versions of numbers can be written by rounding them off to a specified number of significant figures, (sf), shown in orange. 89=90 (1 sf) 0.013=0.01 (1 sf) 789.3=800 (1 sf) 45=50 (1 sf) 2.0009=2.00 (3 sf) 438=440 (2 sf) 0.000889=0.00089 (2 sf) 999.99=1000 (1 sf) Use this form to round a number to a required number of significant figures and check your answer. The correct answer is shown when you are wrong. Press the button to get started. to sf =