Numerical computation papers at this level usually look alike from school to school. Expect a written exam of about 2 to 3 hours with five to seven questions, and a choice: often one compulsory question (commonly 20 to 30 marks) plus any two or three of the rest (usually 10 to 20 marks each), or simply "answer any four". Here is the comforting part: the paper is mostly calculation, and the calculations come from a short, predictable menu.

Root-finding to a tolerance: "find the root correct to 2 (or 3) decimal places" by Bisection, False Position (Regula Falsi), Newton-Raphson or the Secant method. A bracketing method is a favourite for the compulsory question.
A 3×3 linear system by a named method: Gaussian elimination, the Row Echelon method or Gauss-Jordan. Two such questions on one paper is common; Jacobi or Gauss-Seidel iteration turns up now and then.
Short matrix parts (about 5 marks each): multiply two matrices, evaluate a determinant, reduce a matrix to diagonal form.
Theory parts (3 to 8 marks): define absolute, relative and percentage error; distinguish round-off from truncation error; list sources of error; derive the Newton-Raphson formula or state its order of convergence; list the elementary row operations.

Master those few procedures and you can pick your questions with confidence. The marks live in the working: state $f(x)$, show the sign change, write the formula before any numbers, lay iterations out in a neat table carried to 4 decimal places, label every row operation ($R_2 \to R_2 - 2R_1$), and finish with a clear final answer plus a one-line check (substitute back, or compare two successive iterates). Always use the method the question names; the right answer by a different method usually scores very little.

A calm plan for the day: read the whole paper first and choose your optional questions before you write anything. Share your time in proportion to the marks (on a 3-hour paper with a 25-mark compulsory question, roughly 45 minutes for it and 35 to 40 minutes for each of the others), and keep ten minutes at the end to re-check arithmetic. Before the exam, practise on the calculator you will actually use: know where the log (base 10), ln and $e^x$ keys are, keep it in radian mode for any trigonometric function, and use its memory or answer key so that you never round intermediate values to 2 decimal places. Carry 4 dp through every step and round only the final answer.