How to use standard form and round to significant figures on a Casio ClassWiz or fx-CG50
Type numbers like 3.2 × 10⁵ correctly, show answers in standard form and round to 3 significant figures without losing accuracy. Exact keystrokes for the Casio ClassWiz first (the fx-991EX and fx-991CW have different menus, so each has its own tab), then the graphic calculators, a worked example you can check your answers against, the mistakes that cost marks, and the same thing in Desmos.
When you need it
Standard form calculations (very large and very small numbers, often in context) and "give your answer correct to 3 significant figures" on the calculator papers. Write the answer as a × 10n, never as the calculator's E notation.
Practise it: Indices and standard form.
Keystrokes on your calculator
Pick your calculator: the page remembers it next time.
Standard form and rounding on the Casio fx-991EX ClassWiz
Written for the fixed ROM (these models take no OS updates). Casio fx-991EX ClassWiz: scientific (no graphs).
- Type 3.2 × 10⁵ as 3.2 ×10ˣ 5, then × 4.5 ×10ˣ (−) 2 =: 14400.
- To show answers in standard form: SHIFT MENU (SETUP), choose Number Format, then Sci, and give the number of significant figures (3). The answer shows as 1.44 × 10⁴.
- Back to normal: SHIFT MENU → Number Format → Norm.
- Sci (significant figures) and Fix (decimal places) only change what is displayed: the calculator keeps the full value for the next step.
- ENG shows the answer with a power of ten that is a multiple of 3.
Standard form and rounding on the Casio fx-991CW ClassWiz
Written for the fixed ROM (these models take no OS updates). Casio fx-991CW ClassWiz: scientific (no graphs); the newer ClassWiz with a HOME menu of apps.
- Type 3.2 ×10ˣ 5 × 4.5 ×10ˣ (−) 2 and EXE: 14400.
- To show answers in standard form: SETTINGS → Calc Settings → Number Format → Sci, and choose 3 significant figures (1 to 10). SCI shows on the screen while it is on.
- Back to normal: Number Format → Norm (it cancels Fix and Sci).
- Fix (0 to 9 decimal places) and Sci round only the display; the full value is kept.
- If you type powers of ten with ^ instead of ×10ˣ, bracket each number: 4 × 10^7 ÷ 3 × 10^8 without brackets is worked out left to right and gives the wrong answer.
Standard form and rounding on the Casio fx-CG50
Written for OS 3.80 (menus unchanged from OS 3.60 onwards as far as we can tell). Casio fx-CG50: graphic (GDC).
- MENU 1 (RUN-MATRIX). Type 3.2 ×10ˣ 5 × 4.5 ×10ˣ (−) 2 EXE: 14400.
- To show answers in standard form: SHIFT MENU (SET UP), move down to Display, choose Sci and enter the number of significant figures (3; 0 means 10). EXIT.
- Back to normal: SET UP → Display → Norm.
- Fix, Sci and Norm change only the display: internally the calculator still uses a 15-digit mantissa.
Standard form and rounding on the TI-84 Plus CE
Written for OS 5.8.x. TI-84 Plus CE: graphic (GDC); also the TI-84 Plus CE Python / CE-T Python Edition.
- Type 3.2 2nd , (EE) 5 × 4.5 2nd , (−) 2 enter: 14400. On screen 3.2E5 means 3.2 × 10⁵.
- To show answers in standard form: mode, choose SCI on the NORMAL SCI ENG line, and 2 on the FLOAT line (2 decimal places, so 3 significant figures in SCI). 2nd mode (QUIT).
- The answer shows as 1.44E4: write it as 1.44 × 10⁴.
- Set NORMAL and FLOAT again afterwards, or every later answer is rounded to 2 decimal places.
Standard form and rounding on the TI-Nspire CX II
Written for OS 6.x. TI-Nspire CX II: graphic (GDC), non-CAS; the CX II CAS is not allowed in IB, A Level or IGCSE exams.
- On a Calculator page type 3.2·10^5·4.5·10^(−2) and enter: 14400.
- To show answers in standard form: home/on → Settings → Document Settings, set Exponential Format to Scientific. Display Digits sets how many digits you see (Float, Float1 to Float12, Fix0 to Fix12).
- The answer shows as 1.44E4: write it as 1.44 × 10⁴.
For teachers: Show on the board Print a keystroke card Teaching GDC skills
Worked example
(a) Work out (3.2 × 10⁵) × (4.5 × 10⁻²) in standard form. (b) Work out (6.02 × 10²³) ÷ (3.1 × 10⁴), giving your answer in standard form to 3 significant figures. (c) Round 0.00456782 to 3 significant figures and write it in standard form.
Answers (checked with Python)
(a) 14400 = 1.44 × 10⁴. (b) 1.9419… × 10¹⁹ = 1.94 × 10¹⁹ (3 s.f.). (c) 0.00457 = 4.57 × 10⁻³ (the zeros after the decimal point are not significant).
Common calculator mistakes
- Writing the calculator's E notation (1.44E4) as the answer: write 1.44 × 10⁴.
- Typing powers of ten as × 10 ^ without brackets in a division: (6.02 × 10²³) ÷ (3.1 × 10⁴) needs the brackets, or use the ×10ˣ key.
- Rounding in the middle of a calculation: keep the full value (Ans or a stored letter) and round only the final answer.
- Counting the zeros at the start of 0.00456782 as significant figures: 3 s.f. is 0.00457.
- Leaving Sci or Fix switched on for the next question, which then shows rounded values you did not ask for.
Do it in Desmos
Not in the exam. Desmos is not allowed in IGCSE exams. Use it to learn, to check an answer and to see the graph behind a question.
- Type the calculation with brackets: (3.2·10^5)(4.5·10^(−2)).
- Desmos shows very large and very small answers in standard form automatically (with ×10).
Open desmos.com/calculator (free, in any browser) and type:
(3.2·10^{5})(4.5·10^{-2})frac{6.02·10^{23}}{3.1·10^{4}}
Questions
Can I use a calculator for standard form and rounding in the exam?
On Pearson Edexcel International GCSE Maths A (4MA1), yes: Paper 1H and Paper 2H both allow a calculator with no CAS. On Cambridge IGCSE 0580 (from 2025), Papers 1 and 2 are non-calculator and Papers 3 and 4 allow one.
What are the fx-991EX keystrokes for standard form and rounding?
Type 3.2 × 10⁵ as 3.2 ×10ˣ 5, then × 4.5 ×10ˣ (−) 2 =: 14400. Then To show answers in standard form: SHIFT MENU (SETUP), choose Number Format, then Sci, and give the number of significant figures (3). The answer shows as 1.44 × 10⁴. Then Back to normal: SHIFT MENU → Number Format → Norm. The full steps and the other calculators are in the keystrokes section above.
Does this work on other calculators?
Yes. This page has keystrokes for the Casio fx-991EX ClassWiz, Casio fx-991CW ClassWiz, Casio fx-CG50, TI-84 Plus CE and TI-Nspire CX II. The worked example has the same answers on every model, so use it to check.
What should I write as working?
Write the maths, not the key presses: say what you are finding in normal notation (the equation, the probability statement or the integral), then the calculator's answer to the accuracy the question asks for (often 3 significant figures). Keep full accuracy in later parts.
More calculator skills
What else is free here
- IGCSE revision notesEvery Edexcel 4MA1 sub-topic in plain English, with a worked example.
- Past papers and mark schemesLinks to the boards' own papers, with a timer and topic practice.
- Formula sheets (PDF)Edexcel 4MA1 and Cambridge 0580 on one page each, marking what the exam paper gives you.
- Where students lose marksA summary of the examiners' published reports, so you avoid the common slips.
Save your scores and practise the questions that use thisA free account remembers the questions you have done and brings you back to this page.
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Sources
- Casio fx-991EX / fx-570EX Quick Start Guides : Casio fx-991EX ClassWiz, the fixed ROM (these models take no OS updates).
- Casio fx-991CW / fx-570CW User's Guide : Casio fx-991CW ClassWiz, the fixed ROM (these models take no OS updates).
- Casio fx-CG50 Software User's Guide, OS 3.70 (PDF) : Casio fx-CG50, OS 3.80 (menus unchanged from OS 3.60 onwards as far as we can tell).
- TI-84 Plus CE guidebook (Texas Instruments) : TI-84 Plus CE, OS 5.8.x.
- TI-Nspire CX II guidebooks (Texas Instruments) : TI-Nspire CX II, OS 6.x.
- Desmos Help Center for the Desmos functions.
Menu names are taken from each manufacturer's manual for the models shown. Menus can move slightly between OS updates: if a screen looks different on yours, the manual for your version is the reference, and please tell us so we can update this page. A calculator with no tab here has no checked steps for this skill yet. Worked-example answers were recomputed independently in Python.