Using a CalculatorEdexcel IGCSE Maths: Revision notes

Your calculator follows the same order of operations as written maths: brackets, then powers/roots, then multiplication/division, then addition/subtraction (BIDMAS/BODMAS). If a calculation has several stages, it is usually safer to type the whole expression in one go using brackets, rather than working it out step by step and re-entering rounded numbers.

• Use brackets ( ) to force the calculator to evaluate a part of the expression first, e.g. $\dfrac{3.2 + 5.7}{1.4}$ should be typed as (3.2+5.7)/1.4, not 3.2+5.7/1.4.
• The power key (often $x^{y}$ or $\wedge$) and root keys ($\sqrt{\phantom{x}}$, $\sqrt[3]{\phantom{x}}$) must be used with correct bracket placement, especially when the base or the root itself is an expression.
• Fraction keys let you enter a fraction as one object — use this instead of dividing at the end, as it avoids rounding errors mid-calculation.

Most calculators have a dedicated fraction button (often shown as $\dfrac{\square}{\square}$). This lets you:

• Enter a fraction directly, e.g. $\dfrac{7}{12}$, without converting to a decimal first.
• Add, subtract, multiply and divide fractions and mixed numbers, with the calculator giving an exact simplified fraction as the answer.
• Convert between an improper fraction and a mixed number using the $S \leftrightarrow D$ or $\dfrac{a}{b} \leftrightarrow a\dfrac{b}{c}$ key.
• Convert a fraction answer to a decimal (and back) using the $S \leftrightarrow D$ key — useful when a question asks for a decimal or percentage answer.

Keeping working in fraction form for as long as possible avoids rounding errors that build up when you convert to decimals too early.

Calculators have separate keys for common operations, and mixing them up is a frequent source of errors:

When the power or root applies to a whole expression (not just one number), you must bracket that expression first, e.g. $\sqrt{3.6^{2} + 4.8^{2}}$ is typed as √((3.6)^2+(4.8)^2), not √3.6^2+4.8^2 (which the calculator would read as $(\sqrt{3.6})^{2} + 4.8^{2}$).

Numbers in standard form ($a \times 10^{n}$, where $1 \le a < 10$) are entered using the calculator's standard form key, often labelled $\times 10^{x}$ or EXP — not by typing x, 10 and ^ separately.

• To enter $3.4 \times 10^{5}$, press 3.4, then the $\times 10^{x}$ key, then 5 — do not type x10^5 manually, as this can cause bracket errors in longer calculations.
• The display may show a standard form answer using a small raised number or in the form 3.4E5 or 3.4^05 depending on the model — always convert this into correct $a \times 10^{n}$ notation when writing your answer.
• Calculations mixing standard form and ordinary numbers (e.g. multi-step physics-style questions) should still be entered in one go with brackets where needed.

The display is not always the final answer you should write down.

• Check whether the question asks for an exact answer, a decimal rounded to a given number of decimal places, or a value rounded to a given number of significant figures.
• Never round a value shown on the display and then re-enter the rounded version for a further calculation — this causes rounding error to build up. Use the calculator's memory (Ans, M+/M-, or memory store keys) to carry the exact value through to the next step, and round only at the very end.
• Watch for recurring decimals shown with a dot or bar notation (e.g. $0.\dot{3}$ for $\dfrac{1}{3}$) — write these using the correct recurring decimal notation if asked, not just a truncated decimal.
• Be careful reading negative numbers and standard form indices off the display, as different calculator models show them differently.