Ratios, Percentages, Data and Tolerances
Applying scale, proportion, percentage change, graphs, survey data, angles and tolerance ranges to design evidence.
How to prepare for the GCSE Design and Technology written exam
Move from requirement to evidence, technical principle, comparison and justified decision. Use current board materials separately for the NEA and for full timed-paper rehearsal.
Core concepts
Concept 1
Ratio and scale connect drawings, models and outcomes; length scales directly, area with the square of the factor and volume with the cube.
Exam cue: State the ratio direction and use one consistent scale factor.
Concept 2
Percentages support survey analysis, waste, efficiency, profit or change calculations, but the base value and sample must be identified.
Exam cue: Identify numerator, denominator and base value before calculating a percentage.
Concept 3
Tolerance defines an acceptable range around a nominal value and should reflect function, process capability, fit, cost and measurement uncertainty.
Exam cue: Find upper and lower limits, then judge whether a measured value is acceptable.
Risk pitfalls and guardrails
Reversing drawing-to-real scale.
Guardrail: Do not substitute one board's specialist route or current product claim for the multi-board core, and do not turn written process knowledge into NEA or practical submission material.
Adding percentage points when the question asks for percentage change.
Guardrail: Do not substitute one board's specialist route or current product claim for the multi-board core, and do not turn written process knowledge into NEA or practical submission material.
Assuming tighter tolerance is always better regardless of cost or function.
Guardrail: Do not substitute one board's specialist route or current product claim for the multi-board core, and do not turn written process knowledge into NEA or practical submission material.
Memory anchors
Scale factor
The multiplier relating corresponding dimensions in two representations.
Percentage change
Change divided by original value, multiplied by 100 percent.
Nominal size
The stated target dimension before tolerance is applied.
Tolerance
The permitted variation from a nominal value.
Data interpretation
Extracting patterns and implications while respecting how evidence was collected.
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 scale drawing is 1:4. A 75 mm line represents what actual length?
At scale 1:10, what drawing length represents 650 mm?
Answer all questions to submit.
Next step personalized recommendations
Continue learning
Move forward only after this module is stable.
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