Calculator skills for the exams
Edexcel allows a scientific calculator in all three papers and expects you to use it for distributions, statistics and numerical answers. These are the routines that come up every year, written for the Casio fx-991CW (the current ClassWiz) with the older fx-991EX menu numbers alongside. Each ends with a question to check you can do it.
Routines checked by an Edexcel tutor against the current calculator; if a menu name differs on your model, the sequence is the same.
- Normal distribution
- Binomial distribution
- Mean, standard deviation and regression
- Table of values
- Solving equations
- Numerical integration and differentiation
- Vectors and the modulus
Normal distribution
fx-991CW
- HOME → Distribution → Normal CD
- Enter Lower, Upper, σ and μ (use −1×10⁹⁹ or 1×10⁹⁹ for an open tail)
- EXE gives P(Lower ≤ X ≤ Upper)
- For a value from a probability: Distribution → Inverse Normal, enter Area (the probability to the left), σ, μ
fx-991EX: MENU 7 (Distribution) → 2 Normal CD; MENU 7 → 3 Inverse Normal
What the examiners want written down: Write the probability statement first (P(X < 72)), then the calculator line, then the answer to 4 sf; examiners accept calculator working but award method marks for the written statement if the figure is wrong.
Check yourself: X ~ N(50, 8²). Find P(X > 60) and the value a with P(X < a) = 0.9.
P(X > 60) = 0.1056; a = 60.25 (Inverse Normal, area 0.9).
Binomial distribution
fx-991CW
- HOME → Distribution → Binomial CD (cumulative, P(X ≤ x)) or Binomial PD (a single value)
- Choose Variable, enter x, N and p
- For P(X ≥ x) use 1 − P(X ≤ x − 1); for P(a ≤ X ≤ b) use P(X ≤ b) − P(X ≤ a − 1)
fx-991EX: MENU 7 → 4 Binomial PD, 5 Binomial CD
What the examiners want written down: The commonest lost mark is the "≤ x − 1" step. Write P(X ≥ 7) = 1 − P(X ≤ 6) before you press anything.
Check yourself: X ~ B(20, 0.3). Find P(X = 5) and P(X ≥ 8).
P(X = 5) = 0.1789; P(X ≥ 8) = 1 − P(X ≤ 7) = 0.2277.
Mean, standard deviation and regression
fx-991CW
- HOME → Statistics → 1-Variable (or 2-Variable for regression)
- Enter the data in the column; for a frequency table turn Frequency on in the settings
- OK → 1-Var Results shows x̄, σx (population, divide by n) and sx (sample, divide by n − 1)
- For regression: 2-Variable → y = a + bx → Regression Results gives a, b and r
fx-991EX: MENU 6 (Statistics) → 1-Var; OPTN → 1-Var Calc
What the examiners want written down: Edexcel's standard deviation is σx (divide by n) unless the question says otherwise. Check which one you have written down.
Check yourself: Find the mean and standard deviation of 4, 7, 7, 9, 12, 15.
x̄ = 9; σx = 3.606 (sx = 3.950).
Table of values
fx-991CW
- HOME → Table
- Enter f(x), then Start, End and Step
- Use it to check a sketch, locate a root by sign change, or check iteration values
fx-991EX: MENU 8 (Table)
What the examiners want written down: A sign change found in Table is evidence, but the mark scheme wants the two function values written down with the conclusion "change of sign, so a root lies between…".
Check yourself: Show that x³ − 2x − 5 = 0 has a root between 2 and 2.1.
f(2) = −1, f(2.1) = 0.061; change of sign, so a root lies in (2, 2.1).
Solving equations
fx-991CW
- HOME → Equation → Polynomial for quadratics and cubics (choose the degree, enter the coefficients)
- Equation → Simul Equation for simultaneous linear equations
- For any other equation: in Calculate, type the equation with x, then CATALOG → Equation → Solve (or press SOLVE via the x-value prompt); enter a starting value near the root you want
fx-991EX: MENU 9 (Equation/Func); SHIFT SOLVE
What the examiners want written down: Quadratic and simultaneous solutions from the calculator score full marks only when the question does not say "show" or "use algebra". For a show-that, the working must be written.
Check yourself: Solve 2x² − 7x + 3 = 0, and find the root of x = cos x near 0.7.
x = 3 or 0.5; x = 0.7391.
Numerical integration and differentiation
fx-991CW
- In Calculate: CATALOG → Func Analysis → ∫ (or the ∫ key); enter the function, lower and upper limits
- For a gradient: CATALOG → Func Analysis → d/dx, enter the function and the x-value
- Use these to check an answer found by hand, and for trapezium-rule questions to compare with the exact value
fx-991EX: ∫ and d/dx are on the keypad (SHIFT keys)
What the examiners want written down: Definite-integral questions marked "use calculus" need the written integration; the calculator confirms the figure. Where the integral cannot be done by hand (a question says "use your calculator"), write the integral statement and the value to 3 sf.
Check yourself: Evaluate ∫₀¹ e^(−x²) dx to 3 sf.
0.747.
Vectors and the modulus
fx-991CW
- HOME → Vector → define VctA, VctB (3 components for A-level)
- Calculate magnitude with Abs(VctA), dot product with VctA·VctB (Dot Product in the vector menu)
- Angle between vectors: cos θ = (a·b)/(|a||b|)
fx-991EX: MENU 5 (Vector)
What the examiners want written down: Mechanics questions often want the magnitude and direction of a resultant: use the vector app for |r| and tan⁻¹ for the angle, then state the bearing or angle to the i direction as asked.
Check yourself: Find |2i − 3j + 6k|.
7.
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