1.6 Limits of accuracy
Connect measurement and rounding intervals to appropriate accuracy, upper and lower bounds and valid conclusions.
How to study WJEC GCSE Mathematics and Numeracy
Move from concept and notation to a justified method, show a complete mathematical chain, check scale and units, and interpret the answer in context.
Core concepts
Concept 1
Select a reasonable degree of accuracy and recognise measurement uncertainty.
Exam cue: Confirm the unit, entered tier, calculator condition and available formula list before choosing a method.
Concept 2
Determine upper and lower bounds from rounded values.
Exam cue: Write the interval implied by the stated accuracy before combining bounds in a calculation.
Concept 3
Calculate bounds in problems and avoid premature rounding.
Exam cue: Show a complete mathematical chain, use correct notation and units, and interpret or check the result in its original context.
Concept 4
Current matrix coverage: Unit 1, Unit 3. Read the exact subpoint scope in each applicable unit column.
Concept 5
Foundation content is shown in standard type in the specification; bold additions apply only to Higher Tier.
Risk pitfalls and guardrails
Treating a recorded measurement as exact or using the same bound combination for maximum and minimum results.
Guardrail: The Unit 1 and Unit 3 lists are limited and Unit 2 supplies none; preserve exact values and know all other required relationships.
Assuming that every subpoint in a cross-unit strand appears in all three papers, rather than reading the correct matrix column.
Guardrail: Read the precise subpoint in the applicable unit column; a cross-unit strand does not mean every subpoint appears in every paper.
Using a Higher-only method or expectation for a Foundation entry, or importing the outgoing Mathematics/Mathematics-Numeracy structure.
Guardrail: Standard type applies to Foundation and Higher; bold specification additions are Higher-only. There is no Intermediate Tier.
Memory anchors
Accuracy interval
A rounded value represents a range of possible original values.
Lower bound
The lower bound is the least value consistent with the stated rounding.
Upper bound
The upper bound is the greatest limiting value consistent with the rounding.
Measurement error
Recorded measurements have finite precision and therefore uncertainty.
Premature rounding
Rounding intermediate values too early can make the final answer inaccurate.
Checkpoint rule
Do the check-up only after you can summarize each concept in one sentence and identify one dangerous pitfall from memory.
Knowledge Check (after reading)
Short check-up to confirm understanding of this module.
Check-up Questions
A distance is 120 m to 10 m and a time is 15 s to 1 s. What is the upper speed bound?
A value is truncated to 52 by deleting its decimal part. Which error interval applies?
Answer all questions to submit.
Next step personalized recommendations
Continue learning
Move forward only after this module is stable.
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