Rounding significant figures
The method for rounding to a given number of significant figures is almost identical to the method used for rounding to a given number of decimal places.
Look at the number after the one you're interested in to see whether it is greater or less than \(5\). If it's less than \(5\), round down. If it's \(5\) or more, round up.
Question
Q1. Round \(0.0724591\) to \(3\) significant figures (s.f.)
Q2. Round \(0.2300105\) to \(4\) significant figures (s.f.)
Q3. Round \(648,942\) to \(2\) significant figures (s.f.)
A1.
To round to three significant figures, look at the fourth significant figure. It's a \(5\), so round up.
Therefore, \(0.0724591 = 0.0725\) (\({3}\) s.f.)
A2.
To round to four significant figures, look at the fifth significant figure. It's a \(1\), so round down.
Therefore, \(0.2300105 = 0.2300\) (\(4\) s.f.)
A3.
To round to two significant figures, look at the third significant figure. It’s an \(8\), so round up.
Therefore, \(648,942 = 650,000\) (\(2\) s.f.)
