How to find the mean, standard deviation and quartiles (1-var and 2-var statistics) on a Casio ClassWiz or fx-CG50
On the fx-991EX: MENU → 6 → 1 (1-Variable).On the fx-991CW: HOME → Statistics → 1-Variable.
Mean, standard deviation, quartiles and sums from a list or a frequency table. 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
Mean from a frequency table (including grouped data with midpoints), median and quartiles. The statistics mode does the Σfx ÷ Σf for you; the exam still wants to see the method.
Practise it: IGCSE units (Unit 6: Statistics).
Keystrokes on your calculator
Pick your calculator: the page remembers it next time.
1-variable and 2-variable statistics on the Casio fx-991EX ClassWiz
Written for the fixed ROM (these models take no OS updates). Casio fx-991EX ClassWiz: scientific (no graphs).
Watch the key presses on the fx-991EX14 presses, one at a time
The walkthrough needs JavaScript. The same key presses are in the numbered steps below.
- Frequency column on: SHIFT MENU (SETUP) → ▼ → Statistics → Frequency? → On.
- MENU 6 1 (1-Variable). Type the values in x and the frequencies in Freq.
- OPTN → 1-Variable Calc. Scroll with ▼ for x̄, σx, sx, n, min, Q1, Med, Q3, max.
1-variable and 2-variable statistics 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.
- HOME → Statistics → 1-Variable.
- For a frequency table turn on the Freq column: TOOLS → Frequency → On.
- Type the data, then OK → 1-Var Results. Page down for Q1, Med, Q3, min and max.
1-variable and 2-variable statistics 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 2 (STATISTICS). Values in List 1, frequencies in List 2.
- F2 (CALC) F6 (SET): 1Var XList = List1, 1Var Freq = List2. EXIT.
- F1 (1-VAR). Read x̄, σx, sx and n; scroll down with ▼ for minX, Q1, Med, Q3, maxX and Mod.
- Two variables: put y in List 2 (frequency back to 1), then F2 (2-VAR) for x̄, ȳ, Σxy and so on.
- Grouped data: type the class midpoints as the values.
- Box plot: F1 (GRAPH) F6 (SET), Graph Type: MedBox, then F1 to draw. Outliers are shown if you choose Outliers: On.
- fx-CG50 OS 3.x has a setting for how Q1 and Q3 are worked out (in SET UP). Leave it on the standard setting: it matches the IB and exam-board method (medians of the lower and upper halves).
1-variable and 2-variable statistics 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.
- stat 1: Edit. Values in L1, frequencies in L2.
- stat → CALC → 1: 1-Var Stats. List: L1, FreqList: L2. Calculate.
- Scroll down for n, minX, Q1, Med, Q3, maxX. σx is the population standard deviation; Sx the sample one.
- Two variables: 2: 2-Var Stats with Xlist L1, Ylist L2.
- Frequencies must be whole numbers for the quartiles to be given.
1-variable and 2-variable statistics on the TI-Nspire CX II
Written for OS 6.x. TI-Nspire CX II: graphic (GDC), non-CAS (the CX II CAS is a different model: check the exam rules before using one).
- Lists & Spreadsheet: values in column A (name it x), frequencies in column B (name it f).
- menu → Statistics → Stat Calculations → One-Variable Statistics, Num of Lists 1, OK.
- X1 List: x, Frequency List: f, OK. Read x̄, σx, sx, n, MinX, Q1X, MedianX, Q3X, MaxX.
For teachers: Show on the board Print a keystroke card Teaching GDC skills
Worked example
Scores 2, 3, 4, 5, 6 with frequencies 3, 7, 8, 5, 2. Find n, the mean, the standard deviation and the quartiles.
Answers (checked with Python)
n = 25, x̄ = 3.84, σ = 1.12 (sample s = 1.14310), Q1 = 3, median = 4, Q3 = 5.
Now try it on an exam-style question
Use the keystrokes above on IGCSE-style mean, median and mode questions. Free to try, no sign-up.
Common calculator mistakes
- Forgetting the frequency list: with 1Var Freq = 1 the calculator treats the table as five single values.
- σ vs s: IB and most exam questions want σx (divide by n). s (sx) is the unbiased estimate, only when asked.
- Old data or an old frequency setting left from the last question.
- Using class boundaries instead of midpoints for grouped data.
- Estimates: from grouped data the mean and standard deviation are estimates; say so.
If you get an error
fx-991EX: Math ERROR, Syntax ERROR
Math ERROR A result, or a value you typed, is outside the range the calculator can handle, or you asked for something mathematically impossible, such as dividing by zero. Check: Look for a zero denominator, sin⁻¹ or cos⁻¹ of a number bigger than 1 (often a wrong side or angle in the sine or cosine rule), the log of 0 or of a negative number, and a value stored in a variable earlier that you forgot about. Fix: Casio's advice: check the values you typed, use fewer digits and try again. If a variable is the input to a function, make sure its value is one the function accepts.
Syntax ERROR There is a problem with the format of the calculation. In Matrix and Vector calculations it also appears when the sizes do not suit the operation. Check: A missing or extra bracket, or two operation signs in a row. With matrices or vectors: adding a 2 × 2 to a 3 × 3, or a product whose sizes do not match. Fix: Casio's advice: make the corrections. For matrices and vectors, check the size you set for each one.
fx-991CW: Math ERROR, Syntax ERROR
Math ERROR A result, or a value you typed, is outside the range the calculator can handle, or you asked for something mathematically impossible, such as dividing by zero. Check: Look for a zero denominator, sin⁻¹ or cos⁻¹ of a number bigger than 1 (often a wrong side or angle in the sine or cosine rule), the log of 0 or of a negative number, and a value stored in a variable earlier that you forgot about. Fix: Casio's advice: check the values you typed, use fewer digits and try again. If a variable is the input to a function, make sure its value is one the function accepts.
Syntax ERROR There is a problem with the format of the calculation: it is typed in a form the calculator cannot read. Check: A missing or extra bracket, two operation signs in a row, or a function with nothing after it. Fix: Casio's advice: make the corrections and try again.
fx-CG50: Ma ERROR
Ma ERROR Casio's Math ERROR: the result is outside the allowable calculation range, or you are trying to do an illegal mathematical operation, such as dividing by zero. Check: Look for a zero denominator, sin⁻¹ or cos⁻¹ of a number bigger than 1 (often a wrong side or angle in the sine or cosine rule), the log of 0 or of a negative number, and a value stored in a variable earlier that you forgot about. Fix: Casio's advice: check your input values and change them so the result is within the allowable range.
TI-84 Plus CE: ERR:DOMAIN, ERR:DIM MISMATCH, ERR:INVALID DIM, ERR:SYNTAX, ERR:STAT
ERR:DOMAIN A value given to a function or instruction is outside the values it accepts. In a regression, TI says it means the data do not suit the model you chose. Check: Is every input allowed? σ must be positive, p between 0 and 1, and sin⁻¹ or cos⁻¹ needs a number from −1 to 1. Exponential and power models need positive data. Fix: Change the value that is out of range, or choose a model that suits the data.
ERR:DIM MISMATCH Lists or matrices in the same operation have different sizes (TI's example: multiplying two lists with different numbers of elements). Check: L1 and L2 with different numbers of values (one value missed or typed twice), a frequency list of the wrong length, or matrices whose sizes cannot be multiplied. Fix: Make the lists the same length, or check the size of each matrix.
ERR:INVALID DIM TI's knowledge base: one or more stat plots are turned on, but the lists they use are empty. Check: A stat plot left on from a statistics question, so the error appears when you graph a function. Fix: Turn off the stat plots you are not using, or put the data back in the lists.
ERR:SYNTAX The command contains a syntax error: a misplaced function, argument, bracket or comma. Check: TI points out that subtract − and negative (−) are different keys, and using the wrong one causes this error. Then check the brackets and commas. Fix: Find the misplaced function, argument, bracket or comma and correct it.
ERR:STAT A statistics calculation was tried on lists that are not suitable. A statistical analysis needs at least two data points. Check: An empty or one-value list, or the wrong list named in the command. Fix: Check the lists named in the command and the data in them.
TI-Nspire CX II: Domain error, Dimension mismatch, Syntax error
Domain error An argument must be in a specified domain, and this one is not (TI's example: rand(0)). Check: Is every input allowed? σ must be positive, p between 0 and 1, and sin⁻¹ or cos⁻¹ needs a number from −1 to 1. Fix: Change the value that is out of range.
Dimension mismatch Two or more arguments must have the same dimension and do not (TI's example: [1,2]+[1,2,3]). Check: Lists of different lengths in a statistics command, or vectors or matrices of different sizes. Fix: Make the lists, vectors or matrices the sizes the operation needs.
Syntax error The syntax checker found a problem. Check: A missing bracket or comma. Fix: Correct the expression and try again.
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 data as one list, each value as many times as its frequency: D = [2, 2, 2, 3, 3, …].
- mean(D), stdevp(D) (σ, divide by n), stdev(D) (s, divide by n − 1), quartile(D, 1), median(D), quartile(D, 3).
- Desmos's quartile() may use a different rule from your GDC for some data sets: in the exam the GDC's (medians of the halves) is the one to use.
Open desmos.com/calculator (free, in any browser) and type:
D=[2,2,2,3,3,3,3,3,3,3,4,4,4,4,4,4,4,4,5,5,5,5,5,6,6]mean(D)stdevp(D)stdev(D)quartile(D,1)median(D)quartile(D,3)boxplot(D)
Questions
Can I use a calculator for 1-variable and 2-variable statistics 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 the syllabus says you should have a scientific calculator for Papers 3 and 4.
What are the fx-991EX keystrokes for 1-variable and 2-variable statistics?
Frequency column on: SHIFT MENU (SETUP) → ▼ → Statistics → Frequency? → On. Then MENU 6 1 (1-Variable). Type the values in x and the frequencies in Freq. Then OPTN → 1-Variable Calc. Scroll with ▼ for x̄, σx, sx, n, min, Q1, Med, Q3, max. 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
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.