Discrete random variables (DRVs) and expectation
Understand DRVs with distributions given in the form of a table or function. Evaluate probabilities for a DRV. Evaluate measures of average and spread for a DRV to include mean, variance, standard deviation, mode and median. Understand expectation and know the formulae: E X = x p ; E X2 = x2p ; Var X = E X2 E X 2 Understand expectation of linear functions of DRVs and know the formulae: E aX + b = aE X + b and Var aX + b = a2 Var X Know the formula E g X = g x p Find the mean, variance and standard deviation for functions of a DRV such as E 5X3 ,E 18X 3 ,Var 6X 1 Know the discrete uniform distribution defined on the set 1,2,…,n . Understand when this distribution can be used as a model. Proof of mean and variance of discrete uniform distribution.
Full topic guide: the detailed syllabus page with worked examples and common mistakes lives at studyvector.co.uk/a-level/further-maths/discrete-statistics/discrete-random-variables.
Topic preview: Discrete random variables (DRVs) and expectation
Sample stems from the StudyVector question bank (AQA · Edexcel · OCR) — not generic filler text.
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Coverage and provenance
What this page is based on
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Topic explanation
Discrete Random Variables belongs to Discrete & Statistics in A-Level Further Mathematics. The reliable way to revise it is to learn the trigger condition, write the first method line clearly, and practise enough variations that you can spot when the standard method needs adapting. For Further Maths, pay special attention to proof, notation, and whether a result follows from earlier parts of the question.
Discrete random variables (DRVs) and expectation is easiest to revise when it is treated as a precise exam behaviour, not a loose note-taking category. In A-Level Further Mathematics, the goal is to recognise how the topic appears in a question, identify the command word, and decide what evidence, method, or vocabulary earns marks. StudyVector keeps this page tied to AQA · Edexcel · OCR language where coverage is available, then routes practice towards the same topic so revision moves from explanation into retrieval.
A strong revision session starts with a short recall check. Write down the rule, definition, process, or method linked to Discrete random variables (DRVs) and expectation before looking at any notes. Then answer one exam-style prompt and compare your answer with the mark-scheme logic: did you make a clear point, support it with the right step, and avoid drifting into a nearby topic? This matters because many lost marks come from almost-correct answers that do not match the expected structure.
Use this guide as the first layer: understand the topic, look at the worked examples, complete the mini quiz, then move into full practice. The full StudyVector practice loop is designed to capture whether mistakes are caused by knowledge, method, language, or timing. That distinction is important. If the error is factual, you need reteaching. If the error is method-based, you need a worked retry. If the error is wording, you need command-word calibration. That is how Discrete random variables (DRVs) and expectation becomes a controlled revision target rather than another page in a folder.
Lost marks → repair task
Why marks are usually lost here
These are the error patterns StudyVector looks for after an attempt. The goal is not a generic explanation; it is one repair move and one follow-up question.
Unit, formula, or method slip
Examiner move: Select the correct method and keep units, substitutions, signs, and rounding visible.
Repair drill: Redo the calculation or method line slowly, naming the formula before substituting values.
Missing chain of reasoning
Examiner move: Show the link between point, method, evidence, and conclusion instead of jumping to the final line.
Repair drill: Write the missing because/therefore step, then retry one isomorphic question.
Timing breakdown
Examiner move: Match answer length to marks and avoid over-writing low-mark questions.
Repair drill: Set a one-mark-per-minute cap and write a compact version before expanding.
Mini quiz
Use these checks before full practice. They test topic recognition, exam technique, and whether you can connect the explanation to a marked response.
1. What should you check first when a Discrete random variables (DRVs) and expectation question appears in A-Level Further Mathematics?
- A.The command word and the exact topic focus
- B.The longest paragraph in your notes
- C.A memorised answer from a different topic
2. Which revision action gives the strongest evidence that Discrete random variables (DRVs) and expectation is improving?
- A.Rereading the explanation twice
- B.Answering a timed exam-style question and reviewing lost marks
- C.Highlighting every key phrase in the topic notes
Sample questions
Topic-specific public question previews are still being reviewed. We keep them off public pages until the topic match is safe.
Exam tips
- Read the command word carefully — "explain" needs reasons; "state" expects a short fact.
- For Discrete random variables (DRVs) and expectation, show structured working even when you are practising multiple choice — it builds accuracy under time pressure.
- Mark yourself against the mark scheme style: one clear point per mark, in logical order.
- Come back to this topic after a day or two; short spaced reviews beat one long cram.
Worked examples
Example 1
Modelled exam response
For a Discrete Random Variables question, first classify the problem: what information is given, what form should the answer take, and which rule from Discrete & Statistics applies? Write the method line, carry out each transformation cleanly, then substitute or check the result against the original condition. This creates a mark-scheme-friendly answer even when the arithmetic is demanding.
Example 2
Identify the task before answering
Question type: a Discrete random variables (DRVs) and expectation prompt asks for a clear response in A-Level Further Mathematics. Step 1: underline the command word. Step 2: name the exact part of Discrete random variables (DRVs) and expectation being tested. Step 3: decide whether the mark scheme wants a definition, method, explanation, comparison, or calculation. Why it works: most weak answers fail before the content starts because they answer the topic generally rather than the exact exam task.
Example 3
Turn feedback into a repair task
Suppose your answer shows partial understanding but loses marks for precision. First, rewrite the missing mark as a short target: "I need to state the mechanism, unit, reason, or evidence explicitly." Then answer one similar question without notes. Finally, compare the second attempt with the first and check whether the same mark was recovered. Why it works: Discrete random variables (DRVs) and expectation improves faster when feedback creates a specific retry, not another passive reading session.
Next revision routes from this subject
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Targeted practice plan
- Attempt one standard Discrete Random Variables problem and annotate every theorem, identity, or earlier result you use.Source ID: question_bank:0000605c-9463-45da-9711-3dafe147907e · universal · question_bank:0000605c-9463-45da-9711-3dafe147907e
- Attempt one harder Discrete & Statistics problem where the first method is not obvious; write two possible routes before solving.Source ID: question_bank:0036f4b0-0648-4932-ae4a-1df49605c11d · universal · question_bank:0036f4b0-0648-4932-ae4a-1df49605c11d
- After marking, rewrite the solution in the fewest rigorous steps that still justify every transition.Source ID: question_bank:008ff699-62d0-4dec-86d0-f112f25bb506 · universal · question_bank:008ff699-62d0-4dec-86d0-f112f25bb506
Board-specific sources available
- question_bank:0000605c-9463-45da-9711-3dafe147907e · StudyVector question bank row 0000605c…907e · universal · easy
- question_bank:0036f4b0-0648-4932-ae4a-1df49605c11d · StudyVector question bank row 0036f4b0…c11d · universal · easy
- question_bank:008ff699-62d0-4dec-86d0-f112f25bb506 · StudyVector question bank row 008ff699…b506 · universal · hard
Exact IDs are used only when the row already names a real source. Related IDs mean StudyVector has a matching board and subject paper in the local corpus; they are not treated as official origin proof.
Common mistakes
- Starting calculations before identifying the exact form of the question.
- Skipping algebraic or numerical working that the mark scheme would credit.
- Not checking whether the final answer needs units, exact form, a diagram interpretation, or a stated conclusion.
Exam board notes
AQA, Edexcel and OCR differ in wording and calculator/non-calculator balance. Use this as a method lesson, then check your board specification and past-paper style for exact demand.
FAQs
How do I get better at Discrete Random Variables?
Practise in short sets: one easy recognition question, one standard method question, and one mixed question. After each attempt, mark the first line and the final check separately.
What loses marks in Discrete Random Variables?
Most lost marks come from wrong method selection, missing intermediate steps, or an answer that is mathematically correct but not in the requested form.
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