MGU · MG1DSCBCA103 · Semester 1

Discrete Mathematics

Revision and exam practice

Revise each module, practise answer writing and check your understanding. Questions are based on the supplied syllabus; they are not presented as actual or guaranteed MGU questions.

MODULE CHECKLISTS · QUESTION BANK · ESE FORMAT

Exam pattern and priorities

The syllabus states 60 course hours, 30 CCA marks and a 70-mark ESE (2 hours). In the ESE, answer any 5 of 8 two-mark questions, 5 of 8 six-mark questions and 3 of 6 ten-mark questions. The listed counts by module are: Module I (2,2,2), Module II (2,2,1), Module III (2,2,1), Module IV (2,2,2), for Parts A, B and C. This is the distribution printed in the syllabus; it does not guarantee a particular topic.

MUST MASTER

Truth-table/equivalence problems; set operations and functions; relation properties/equivalence; determinant, inverse and solving systems.

IMPORTANT

Inference rules, function types, relation representations, symmetric/skew-symmetric matrices.

QUICK-SCORE

Definitions, notation, connective meanings, property names and short matrix facts.

Answer strategy

Show truth-table columns, set membership, relation checks, matrix operations and substitution checks. A correct result with clear steps is easier to follow.

MODULE 1 · LOGIC AND PROOFS

Recall checklist

10 core concepts: proposition; negation; conjunction; disjunction; conditional; biconditional; truth table; equivalence; premise/conclusion; inference rule.

Key terms: tautology, contradiction, contingency, logical equivalence, valid argument, modus ponens, modus tollens, converse, inverse, contrapositive.

Rules and formulas: p→q≡¬p∨q; De Morgan’s laws; modus ponens and modus tollens patterns.

Common traps: confuse inclusive “or” with exclusive or; forget p→q is false only for T→F; assume converse is equivalent; affirm the consequent.

MODULE 2 · SET THEORY

Recall checklist

10 core concepts: set; element; subset; empty set; universal set; power set; union; intersection; complement/difference; function.

Key terms: Cartesian product, domain, codomain, range, injective, surjective, bijective, image, preimage, inclusion-exclusion.

Formula: |A∪B|=|A|+|B|−|A∩B|. Check each function property using the stated domain and codomain.

Common traps: union vs intersection; codomain vs actual range; function must have exactly one output per input; onto depends on the codomain.

MODULE 3 · RELATIONS

Recall checklist

10 core concepts: Cartesian product; relation; ordered pair; reflexive; symmetric; antisymmetric; transitive; matrix representation; digraph; equivalence class.

Key terms: relation on a set, loop, adjacency matrix, equivalence relation, partition, related elements, property, counterexample.

Core test: equivalence relation = reflexive + symmetric + transitive. Check all elements/pairs; one counterexample disproves a universal property.

Common traps: symmetry is not antisymmetry; relation is relative to its underlying set; proving only two properties is not enough.

MODULE 4 · MATRICES

Recall checklist

10 core concepts: order; transpose; identity; zero matrix; symmetric; skew-symmetric; matrix operations; determinant; inverse; solution of a non-homogeneous system.

Key terms: square matrix, singular, non-singular, coefficient matrix, constants vector, Cramer’s rule, determinant, inverse, row, column.

Formulas: det([[a,b],[c,d]])=ad−bc; inverse exists when determinant ≠0; AX=B gives X=A⁻¹B when inverse exists; Cramer xᵢ=Dᵢ/D when D≠0.

Common traps: dimensions and order in multiplication; assuming AB=BA; sign errors; using inverse/Cramer when determinant is zero; not checking the solution in original equations.

Expected / Exam-Focused question bank

All prompts below are derived from syllabus topics. They are not represented as past-paper questions.

2-mark questions

  1. Define a proposition and give an example.
  2. When is p→q false?
  3. State one of De Morgan’s laws.
  4. Define a subset or power set.
  5. Define an injective function.
  6. What is a reflexive relation?
  7. State the three properties of an equivalence relation.
  8. Define a skew-symmetric matrix.
  9. When does a 2×2 matrix have an inverse?
  10. State the condition for Cramer’s rule to give a unique solution.

6-mark questions

  1. Construct a truth table and determine whether two propositions are equivalent.
  2. Apply inference rules to decide whether a conclusion follows from given premises.
  3. Perform set operations and solve a finite set-counting problem.
  4. Determine whether a given function is one-to-one or onto.
  5. Test reflexive, symmetric, antisymmetric and transitive properties of a relation.
  6. Represent a relation by a matrix or digraph and interpret it.
  7. Find a 2×2 determinant and inverse, showing each step.
  8. Solve a pair of linear equations using Cramer’s rule.

10-mark questions

  1. Use truth tables and propositional equivalences to analyse a compound statement and justify the result.
  2. Analyse a relation for its properties; determine whether it is an equivalence relation and find its classes.
  3. Carry out matrix operations, find an inverse and solve a non-homogeneous system using the matrix method.
  4. Solve a suitable system using Cramer’s rule and verify the result.

Model answer structure

2 marks: state the definition or rule accurately, then add one property/example.

6 marks: show definition, method, working (truth table/set/property checks/calculation) and a brief conclusion.

10 marks: introduce the relevant method, show complete organised working, justify each important step, state the answer clearly and verify where possible.

7-day revision plan

DayFocus and task
1Propositions, connectives and truth tables; complete 3 truth tables.
2Equivalences and inference; explain why one invalid argument fails.
3Sets and operations; solve one inclusion-exclusion problem and function classification.
4Relations and representations; check all properties and equivalence classes.
5Matrix types, operations, determinants and inverse calculations.
6Systems by inverse matrix and Cramer’s rule; check solutions.
7Mixed timed 2-, 6- and 10-mark practice; review errors.

14-day revision plan

DayFocus
1Propositions and translating statements into symbols.
2Connectives and truth tables.
3Logical equivalences and De Morgan’s laws.
4Rules of inference and invalid arguments.
5Set notation, membership and subsets.
6Set operations and counting applications.
7Functions: domain, codomain, range and types.
8Relations and property checks.
9Matrix and digraph representations; equivalence relations.
10Matrix definitions, types, transpose and operations.
11Determinants and inverse.
12System solving by matrix method.
13Cramer’s rule and verification.
14Mixed timed answers, formula/definition recall and error correction.

Final 24-hour checklist

If you can do these things, you are exam ready: explain the rule, apply it to a new problem, show enough working for another person to follow, and check the result.

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