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Casio fx-991 ClassWiz

GCSE & A-level

Advanced scientific calculator · organised by the exam question that needs it.

The advanced scientific calculator — fractions, standard form, statistics, the equation solver and tables of values, organised by the exam question that needs them.

Steps are for the ClassWiz fx-991 (EX and CW). On the fx-991EX the settings menu is SHIFT then SETUP; on the newer fx-991CW use the dedicated SETTINGS key (the menu names are the same). The equation solver and numerical calculus are ClassWiz features the basic GCSE fx-83GT/85GT models don't have — but those do have fractions, statistics, standard form and a table of values, with the same steps.

Number

Standard form (powers of ten)

When to use: Enter or calculate with numbers in standard form, e.g. a physics or number question written as a × 10ⁿ.

  1. 1Type the number part, e.g. 3.2
  2. 2Press the ×10ˣ key — This is the dedicated standard-form key — do NOT type '× 1 0 ^'.
  3. 3Type the power, e.g. 5, then = — 3.2 ×10ˣ 5 means 3.2 × 10⁵.
  4. 4To show answers in standard form: SHIFT SETUP → Number Format → Sci — On the fx-991CW use the SETTINGS key instead of SHIFT SETUP.

Work out (3 × 10⁵) × (2 × 10³).

3 ×10ˣ 5×2 ×10ˣ 3=

Answer: 6 × 10⁸

  • Using the ×10ˣ key keeps the whole '× 10 to the power' as one number, so the order of operations is right; typing 10^ separately is where marks get lost.
  • If the display shows a long decimal, switch Number Format to Sci to read it back as standard form.

Fractions and exact ↔ decimal

When to use: Keep a value as an exact fraction or surd, or convert between a fraction and its decimal.

  1. 1Use the fraction template key to enter a fraction (numerator, ▼, denominator)
  2. 2Press = to get the answer in its exact form
  3. 3Press the S⇔D key to toggle between the exact fraction/surd and the decimal

Write 0.375 as a fraction.

0.375=S⇔D

Answer: 3/8

  • S⇔D converts terminating decimals to fractions and surds to decimals — handy to check an exact answer.
  • If a 'give an exact answer' question shows a decimal, press S⇔D to get the fraction or surd the mark scheme wants.

Equations & algebra

Solve quadratics, cubics and simultaneous equations

When to use: Solve a quadratic/cubic or a set of simultaneous linear equations and you only need the answer (or a check).

  1. 1MENU → Equation (Equation/Func)
  2. 2Choose Simultaneous (2–4 unknowns) or Polynomial (degree 2–4)
  3. 3Type each coefficient, pressing = after each
  4. 4Press = to read out each solution

Solve x² − 5x + 6 = 0.

MENU → EquationPolynomial, degree 21 = , −5 = , 6 ==

Answer: x = 3 and x = 2

  • This is a ClassWiz feature — the basic GCSE fx-83GT/85GT cannot do it, so don't rely on it in a shared-calculator setting.
  • For 'solve algebraically' or 'show that', the calculator answer scores nothing without the factorising/formula/elimination working.

Table of values (for graphs and roots)

When to use: Fill in a table of values to draw a graph, or locate a root by looking for a change of sign.

  1. 1MENU → Table
  2. 2Type the function as f(X), then =
  3. 3Enter Start, End and Step when prompted
  4. 4Scroll the table to read each value — A sign change between two rows means a root lies between them.

Show that x² − 3 = 0 has a root between x = 1 and x = 2.

MENU → Tablef(X) = X² − 3, =Start 1, End 2, Step 1read f(1) and f(2)

Answer: f(1) = −2 and f(2) = 1: the sign changes, so there is a root between 1 and 2

  • The change-of-sign argument is the written method — quote both values and say the sign changes, don't just point at the calculator.
  • Use a small Step (e.g. 0.1) to trap a root more tightly for a decimal-search question.

Solve a non-polynomial equation numerically

When to use: An equation involving exponentials, logarithms or trig has no convenient algebraic solution and you need a numerical root or a check.

  1. 1fx-991CW: HOME → Equation → Solver
  2. 2fx-991EX: MENU → Calculate → enter the equation → SHIFT CALC (SOLVE)
  3. 3Enter the equation and choose the target variable — On the EX, the target variable is the X in the expression.
  4. 4Enter a starting value near the expected root, then Execute / =

Solve eˣ = 5, using 1 as the starting value.

Open SolverEnter eˣ = 5Target: xInitial value: 1Execute / =

Answer: x ≈ 1.60944

  • Solver uses a numerical method and may return only the root near your starting value; change the start to search for another root.
  • A numerical answer does not replace the required iteration, sign-change or rearrangement working in a method-mark question.

Solve a polynomial inequality

When to use: A quadratic, cubic or quartic inequality asks for the interval(s) of x that make an expression positive, negative or zero.

  1. 1fx-991CW: HOME → Inequality · fx-991EX: MENU → Inequality
  2. 2Choose the polynomial degree (2, 3 or 4)
  3. 3Choose <, >, ≤ or ≥ to match the question
  4. 4Enter the coefficients in descending powers of x, then Execute / =

Solve x² + 2x − 3 ≥ 0.

Inequality → degree 2Choose ax² + bx + c ≥ 0a = 1, b = 2, c = −3Execute / =

Answer: x ≤ −3 or x ≥ 1

  • Select the inequality direction carefully — ≥ and ≤ include the boundary roots.
  • Sketch a sign diagram or parabola when reasoning is assessed; the interval display is a strong final check.

Statistics

Mean and standard deviation

When to use: A list of data or a frequency table, and the question asks for the mean or standard deviation.

  1. 1MENU → Statistics → 1-Variable
  2. 2For a frequency table, first turn Frequency On — SHIFT SETUP → Statistics → Frequency: On (fx-991CW: use the SETTINGS key).
  3. 3Type the values (and their frequencies) into the table
  4. 4Press AC, then OPTN → 1-Variable Calc — Reads x̄ (mean), σx (population sd), sx (sample sd), Σx, n.

Find the mean and population standard deviation of 2, 4, 4, 4, 5, 5, 7, 9.

MENU → Statistics → 1-VariableEnter the eight valuesAC, then OPTN → 1-Variable Calc

Answer: mean x̄ = 5, population sd σx = 2 (sample sd sx ≈ 2.14)

  • σx is the population standard deviation; sx is the sample one — check which the question wants.
  • Turn Frequency On before entering a frequency table, or every value is counted once.

Regression line and correlation

When to use: Bivariate data: find the equation of the line of best fit y = a + bx, or the correlation coefficient r.

  1. 1MENU → Statistics → y = a + bx
  2. 2Type the x-values and y-values into the two columns
  3. 3Press AC, then OPTN → Regression Calc — Gives a, b and r.
  • r close to ±1 is strong linear correlation; close to 0 is weak.
  • Use the y = a + bx line to predict within the data range only — extrapolation is a written-answer trap.

Trigonometry

Degrees vs radians (and inverse trig)

When to use: Any trig calculation — and the single most common calculator error in the exam.

  1. 1SHIFT SETUP → Angle Unit → Degree or Radian — On the fx-991CW use the SETTINGS key instead of SHIFT SETUP.
  2. 2Check the small D or R indicator at the top of the screen
  3. 3For an angle from a ratio, use SHIFT then sin / cos / tan (sin⁻¹ etc.)
  • GCSE and A-level mechanics/geometry are in degrees; A-level trig/calculus questions are usually in radians — set the mode to match before you start.
  • If an answer is wildly wrong (e.g. an angle of 0.5 where you expected 30), you are almost certainly in the wrong angle mode.

Calculus (A-level)

Definite integral and gradient at a point

When to use: Check a definite integral, or the value of dy/dx at a particular x — the ClassWiz does both numerically.

  1. 1For an integral: press the ∫ key
  2. 2Enter the lower limit, upper limit and the expression, then = — e.g. ∫ from 0 to 2 of X² dX.
  3. 3For a gradient: press the d/dx key, enter the expression and the x-value, then =

Evaluate the integral of x² from 0 to 2.

∫ keylower 0, upper 2, expression X²=

Answer: 8/3 ≈ 2.667

  • These give a number, not the algebra — an A-level 'integrate' or 'differentiate' question still needs the worked method for the marks.
  • Great for checking your by-hand answer before you commit to it.

Sequences & series

Evaluate a finite sum with Σ

When to use: A sequence or series question gives a term in r and asks for the sum between two integer limits.

  1. 1Open Calculate
  2. 2fx-991CW: CATALOG → Func Analysis → Summation (Σ)
  3. 3fx-991EX: press SHIFT then the key marked Σ
  4. 4Fill in the term, index variable, lower limit and upper limit, then =

Evaluate Σ(3r − 1) from r = 1 to r = 20.

Insert the Σ templateterm 3X − 1lower 1, upper 20=

Answer: 610

  • Use the same index and limits as the question; starting at 0 instead of 1 adds an unwanted term.
  • Use the total to check your series formula, but show that formula when the question awards method marks.

Distributions (A-level)

Binomial and normal distribution lookups

When to use: An A-level statistics question asks for a binomial or normal probability, or for a normal value from a given cumulative area.

  1. 1fx-991CW: HOME → Distribution · fx-991EX: MENU → Distribution
  2. 2Choose Binomial CD for P(X ≤ x), or Normal CD / Inverse Normal as required
  3. 3For Binomial CD choose Variable, then enter x, N and p
  4. 4Select Execute / press =

X ~ B(20, 0.3). Find P(X ≤ 5).

Distribution → Binomial CD → Variablex = 5N = 20p = 0.3Execute / =

Answer: ≈ 0.416371

  • For P(X < k) on a discrete distribution, enter k − 1 in Binomial CD; P(X ≤ k) uses k.
  • Normal menus ask for σ, not σ². Inverse Normal uses a cumulative left-tail area, so convert an upper-tail percentage first.

Complex numbers (Further Maths)

Calculate with complex numbers

When to use: Further Maths: check arithmetic with a + bi, or find a complex number's modulus, argument or conjugate.

  1. 1fx-991CW: HOME → Complex · fx-991EX: MENU → Complex
  2. 2Set Complex Result to a+bi — Set the angle unit first if you need an argument or polar form.
  3. 3fx-991CW: CATALOG → Complex → i · fx-991EX: OPTN → i
  4. 4Enter the expression with brackets, then Execute / =

Evaluate (3 + 4i) ÷ (1 − i) in the form a + bi.

Open ComplexComplex Result: a+biInsert i from the Complex menu(3 + 4i) ÷ (1 − i)Execute / =

Answer: −1/2 + 7i/2 (that is, −0.5 + 3.5i)

  • Use the Complex app: the CW Calculate app cannot accept i as the imaginary unit.
  • The calculator confirms arithmetic, but show conjugate multiplication or modulus-argument working when method marks are available.

Vectors (A-level & Further Maths)

Store vectors and find a dot product

When to use: A vectors question asks for arithmetic, a scalar product, perpendicularity or the angle between two vectors.

  1. 1fx-991CW: HOME → Vector · fx-991EX: MENU → Vector
  2. 2Define VctA: choose its dimension and enter each component
  3. 3Define VctB in the same way, then return to the calculation screen
  4. 4fx-991CW: CATALOG → Vector → Vector Calc → Dot Product
  5. 5fx-991EX: OPTN → Vector → Dot Product → enter VctA and VctB → =

Find (1, 2, 3) · (4, −1, 2).

Define VctA = (1, 2, 3)Define VctB = (4, −1, 2)Choose Dot ProductVctA, VctB=

Answer: 8

  • Both vectors must have the same dimension for a dot product.
  • Use the value to check perpendicularity or cos θ, but write the vector formula and substitution for method marks.

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