What's the Difference Between Decimal Places and Significant Figures?

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To round, keep the required digits and inspect the next digit. If that digit is $5$ or greater, increase the final retained digit by $1$.

Zeros require care. Zeros between non-zero digits are significant, so $2.03$ has three significant figures. Trailing zeros after a decimal point are also significant, so $4.500$ has four. However, trailing zeros in a whole number such as $1200$ may be ambiguous unless the required accuracy or standard form is stated.

A common misconception is that leading zeros are significant. They are not: in $0.0032$, only $3$ and $2$ are significant. To show precision clearly when trailing zeros may be ambiguous, use standard form: $1.2 \times 10^3$ has exactly two significant figures.

IB Exam Technique

This is part of SL 1.6, Approximating and estimating and applies to SL and HL on every GDC-active paper. Follow the accuracy instruction exactly, keep full GDC precision during working, and round only the final answer; premature rounding can cause the final accuracy mark to be lost.