IGCSE Calculator Skills
Most impossible calculator answers come from one of three causes: the wrong angle mode, a missing bracket, or a rounded value re-entered by hand. All three are avoidable habits rather than knowledge gaps.
A scientific calculator is assumed on several IGCSE papers, and marks are lost to operation rather than to method. This sheet covers the settings and habits that prevent those losses.
Modes and settings to check
| Setting | When it matters | How to spot the error |
|---|---|---|
| Degree mode | Trigonometry stated in degrees, which covers most of 0580 | sin 30 should give 0.5, not minus 0.988 |
| Radian mode | Circular measure and calculus in 0606 | sin 1.5 should give 0.997, not 0.026 |
| Normal display | General working | Answers appearing as unexpected fractions or surds |
| Standard form display | Very large or very small numbers | Numbers shown with an unfamiliar exponent notation |
| Clear memory | Start of every question | A previous answer contaminating a new calculation |
Keys worth knowing
| Key | What it does | Typical use |
|---|---|---|
| ANS | Recalls the previous answer exactly | Chaining calculations without rounding |
| Memory store | Saves a value for later | Holding an unrounded intermediate result |
| Fraction key | Enters and displays exact fractions | Keeping answers exact rather than decimal |
| Powers key | Raises to any power | Compound interest and index calculations |
| Root keys | Square root, cube root and general roots | Surds and fractional indices |
| Inverse trigonometry | Finds an angle from a ratio | Use when two sides are known and an angle is wanted |
| EXP or times ten to the x | Enters standard form directly | Avoids typing long strings of zeros |
| Bracket keys | Controls the order of operations | Any fraction with more than one term above or below |
Errors that produce impossible answers
| Symptom | Likely cause | Fix |
|---|---|---|
| A negative length or a negative magnitude | A sign error, or squaring skipped | Recheck the substitution |
| An angle above 90 in a right-angled triangle | Ratio inverted, or the wrong ratio chosen | Relabel the triangle and reselect |
| A probability greater than 1 | Wrong denominator, or terms added that should be multiplied | Recheck against the total number of outcomes |
| An efficiency above 100 per cent | Input and output divided the wrong way round | Useful output goes on top |
| A wildly large or small value | A missing bracket in a fraction | Bracket the whole numerator and denominator |
| Trigonometric value slightly off | Rounded value re-entered by hand | Use ANS or memory instead |
How to use this sheet
- Check the angle mode at the start of every session and again whenever a trigonometric answer looks odd.
- Bracket the entire numerator and the entire denominator of any fraction you type in.
- Use ANS or memory to carry values forward instead of retyping rounded numbers.
- Sense check every answer before writing it down. Impossible values are usually operation errors, not method errors.
- Learn your own calculator before the exam. Models differ, and the exam is not the time to explore the menus.
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Frequently asked questions
How do I know if my calculator is in the wrong mode?
Test it with a value you know. The sine of 30 degrees is exactly 0.5, so if degree mode is set that is what appears. If you see minus 0.988 instead, the calculator is interpreting 30 as radians and the mode needs changing.
Why do I need brackets when typing a fraction?
Calculators follow the order of operations, so typing a fraction without brackets divides by the first term only. Bracketing the whole numerator and the whole denominator forces the calculator to evaluate each fully before dividing.
Should I retype an intermediate answer?
No. Use the ANS key or the memory to carry the exact value forward. Retyping a rounded intermediate value introduces error that can shift the third significant figure of the final answer and cost the accuracy mark.
What should I do if an answer looks impossible?
Check the units and the mode before checking the method. Negative lengths, probabilities above one and efficiencies above one hundred per cent are almost always caused by an inverted fraction, a missing bracket or the wrong angle mode.
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Other reference sheets
Written to the published Cambridge IGCSE syllabuses. Always check the formula list and data sheet issued with your own paper, since the material provided differs between subjects and syllabus versions. Last reviewed 2026-08-12.