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.
You 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.
Q1. Round 0.0724591 to 3 significant figures (s.f.)
Q2. Round 0.2300105 to 4 significant figures (s.f.)
To round to three significant figures, look at the fourth significant figure. It's a 5, so round up.
Therefore, 0.0724591 = 0.0725 (3s.f.)
To round to four significant figures, look at the fifth significant figure. It's a 1, so round down.
Therefore, 0.2300105 = 0.2300 (4s.f.)
Even though 0.2300 is the same as 0.23, include the zeros to show that you have rounded to 4 significant figures.
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