Use scale plans and check reproduced scales
Use a scale plan in both directions and explain why a resized copy needs a new effective scale.
Section 4.11 · Similarity
Exam scope and assessment notes
The first four lessons are shared Foundation content inherited by Higher; the last three are additional Higher area, volume and mixed-similarity work. Match corresponding vertices and keep one positive length factor in a stated direction. Maps and plans use exact stated lengths; screen centimetres, physical ruler accuracy and print calibration are not certified. Similar solids require corresponding dimensions to scale together; total surface area includes the whole stated external boundary. Exact numerical comparisons and text-entry attempts do not approve written proof, marks, mastery or physical construction. Linear 4MA1 Issue 2 is checked against November 2026/June 2027 entries; regional options depend on centre eligibility and modular awards remain separate. Publisher links are navigation only: literal Book2 Shape and Space6 F4.11B, Shape and Space7 F4.11A, and Shape and Space9 H4.11A/B/C tags are retained, with no Book1 tag invented. The map/proof page and topic-location conflicts remain explicit; the relevant chapter/Hub bodies are unavailable. Full-book, specialist and formal-assessment approval remain pending.
Before you begin
- Interpret a map or plan ratio using a common length unit.
- Convert between centimetres and metres.
- Express a percentage of an original linear size as a multiplier.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
The same wall is drawn at 1:30 and 1:90. Which drawing shows the longer wall on paper?
What you will learn
- Calculate real dimensions and required drawing dimensions from a plan scale.
- Compare two plans of the same real object.
- Recover the effective scale after a stated uniform change in printed linear size.
A room plan is drawn at 1:80. A wall is 6.5 cm on the plan; a real door is 0.9 m wide. Find the real wall length and the required door width on the plan.
Construct your own complete figures, directed routes and corner correspondence. Enter every requested quantity, substitution and reason; missing outlines, dimensions and scale factors remain your own work.
Given panel 1 — drawing unit: cm
Blue: original supplied geometry. Amber: my actual submitted work. Each frame uses its stated drawing unit; compare mixed units by conversion, not by apparent screen size. Unlabelled sides and angles stay for calculation.
Both drawing axes have equal scale in cm. Whole-view turns rotate all geometry together; free points retain actual coordinates without snapping.
A room plan is drawn at 1:80. A wall is 6.5 cm on the plan; a real door is 0.9 m wide. Find the real wall length and the required door width on the plan.
Only literal givens are initially labelled. Every requested scalar, complete missing outline, chosen correspondence and explained reference remains learner work.
Compare other given figures in their stated units
Frames with the same unit and dimension share a drawing scale. Different units use separate labelled metric frames; convert physical lengths rather than comparing apparent screen sizes.
Given panel 2 — drawing unit: cm
Blue: original supplied geometry. Amber: my actual submitted work. Each frame uses its stated drawing unit; compare mixed units by conversion, not by apparent screen size. Unlabelled sides and angles stay for calculation.
Both drawing axes have equal scale in cm. Whole-view turns rotate all geometry together; free points retain actual coordinates without snapping.
A room plan is drawn at 1:80. A wall is 6.5 cm on the plan; a real door is 0.9 m wide. Find the real wall length and the required door width on the plan.
Only literal givens are initially labelled. Every requested scalar, complete missing outline, chosen correspondence and explained reference remains learner work.
Given panel 3 — drawing unit: m
Blue: original supplied geometry. Amber: my actual submitted work. Each frame uses its stated drawing unit; compare mixed units by conversion, not by apparent screen size. Unlabelled sides and angles stay for calculation.
Both drawing axes have equal scale in m. Whole-view turns rotate all geometry together; free points retain actual coordinates without snapping.
A room plan is drawn at 1:80. A wall is 6.5 cm on the plan; a real door is 0.9 m wide. Find the real wall length and the required door width on the plan.
Only literal givens are initially labelled. Every requested scalar, complete missing outline, chosen correspondence and explained reference remains learner work.
Given panel 4 — drawing unit: m
Blue: original supplied geometry. Amber: my actual submitted work. Each frame uses its stated drawing unit; compare mixed units by conversion, not by apparent screen size. Unlabelled sides and angles stay for calculation.
Both drawing axes have equal scale in m. Whole-view turns rotate all geometry together; free points retain actual coordinates without snapping.
A room plan is drawn at 1:80. A wall is 6.5 cm on the plan; a real door is 0.9 m wide. Find the real wall length and the required door width on the plan.
Only literal givens are initially labelled. Every requested scalar, complete missing outline, chosen correspondence and explained reference remains learner work.
Mark or construct the actual complete segment in Given panel 1
No geometry is recorded for this action.
Enter your own count and names in boundary, route or anchor order. A cuboid needs all eight actual corners: base A–B–C–D and corresponding E–F–G–H, with all faces closing. Generic figure and solid drawings are coordinate witnesses, not extra hypotheses for the paper question.
This draft is incomplete: Enter your own integer count between 2 and 2. All entered raw text and points remain visible; no valid replacement figure is invented.
My quantities, equations and reasons
Enter exact supported fractions or decimals. A field asking for a coefficient of π takes the rational coefficient alone. Keep two decimal places where money is requested. Every response or unit edit closes previous feedback and references.
Required for the whole attempt. Give an exact supported scalar.
Required for the whole attempt. Give an exact supported scalar.
Required for the whole attempt.
Written substitutions and reasons require human review; they are not automatically proved or marked.
Required for the whole attempt.
Written substitutions and reasons require human review; they are not automatically proved or marked.
This tool compares fixed mathematics with actual coordinate constructions. Written reasoning needs human review; it awards no marks, mastery, physical-instrument competence, specialist signoff or formal assessment approval. Mixed physical units require conversion; projected 3D angles and lengths are schematic.
A scale plan works in both directions
A scale plan represents real lengths with one stated corresponding-length ratio. Put the plan length and real length in compatible units, then use real=n×plan for a scale of 1:n. If a real width is supplied and its drawn width is required, rearrange the same equation to plan=real/n. Do not apply an area factor to either width.
Different dimensions can require different directions in one problem. A wall length read from a plan may need to be enlarged to a real length, while a real doorway width may need to be reduced to a plan length. Label each known quantity as plan or real before calculating. Your final unit should make clear whether the answer belongs on paper or in the real setting.
Compare plans without changing the object
When the same real object is drawn at two scales, the real length stays fixed. A smaller positive denominator in 1:n gives a larger plan length. Compare the drawn lengths by dividing the same real length by each denominator. This is a statement about the drawing size, not evidence that the building or object itself has changed.
If a finished plan is printed at p times its previous linear size, every printed length becomes p times its former value. Its effective denominator becomes n/p because each new centimetre of paper represents fewer real centimetres when the print is enlarged. Both axes must change by the same factor for a single ordinary scale to remain valid; stretching only one direction requires separate treatment.
Keep the scale tied to the actual copy
A printed scale label can become wrong after resizing even if its text remains visible. A numerical scale calculation therefore needs the scale that applies to the copy being used. A scale bar printed and resized with the whole map can help recover that relationship, provided its stated real length and its actual reproduced length are read appropriately.
These tasks use exact stated lengths and stated uniform print changes. They do not certify screen centimetres, physical ruler accuracy, printing calibration or formal construction competence. Sketching a required plan dimension is useful practice, but an instrument-based drawing must also respect the actual paper size, tool resolution and any tolerance specified by the task. Keep those practical limits separate from the ideal arithmetic.
Sources for this lesson
Pause and explain
A 1:n plan is uniformly printed at p times its original linear size. What is its effective scale?
Worked example
A room plan is drawn at 1:80. A wall is 6.5 cm on the plan; a real door is 0.9 m wide. Find the real wall length and the required door width on the plan.
Show the worked solution
- For the wall, the plan length is known: 6.5×80=520 cm in the room, or 5.2 m.
- For the door, convert the real width first: 0.9 m=90 cm.
- Recover the required plan width by division, 90÷80=1.125 cm. The two calculations run in opposite directions.
- Check the plan dimensions with the same scale: 520/6.5=90/1.125=80.
Answer The real wall length is 5.2 m, and the required door width on the plan is 1.125 cm.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
A 4.8 m wall is shown on plans at 1:50 and 1:100. Calculate each plan length and explain which plan is larger.
Give me a hint
Hold the real wall fixed and divide by each scale denominator.
Compare my reasoning
- The real wall is fixed at 4.8 m=480 cm for both plans.
- At 1:50, divide the unchanged real length by 50 to obtain the plan length, 480÷50=9.6 cm.
- At 1:100, divide that same real length by 100 to obtain the plan length, 480÷100=4.8 cm.
- The 1:50 drawing is larger: the smaller denominator makes the same real length twice as long on paper.
The plan lengths are 9.6 cm at 1:50 and 4.8 cm at 1:100. The 1:50 plan is larger.
Look for these in your work
- Use the same real wall for both plans.
- Calculate both required paper lengths.
- Explain the effect of the denominator on drawing size.
An original 1:60 plan is printed at 150% of its original linear size. Find the effective scale and the new printed length of a wall originally 5 cm on the plan.
Give me a hint
The paper changes size while the represented wall does not. Apply the print multiplier to lengths and reverse it for the denominator.
Compare my reasoning
- A print at 150% of the original linear size has multiplier 150/100=3/2. The real wall does not change.
- The original 5 cm plan wall becomes 5×3/2=7.5 cm on the new print.
- The effective denominator is 60÷(3/2)=40, so the new scale is 1:40.
- Check with the unchanged real length: the original represents 5×60=300 cm=3 m, and the new print represents 7.5×40=300 cm as well.
The effective scale is 1:40 and the new printed wall length is 7.5 cm. The real wall remains 3 m long.
Look for these in your work
- Convert the print percentage to a linear multiplier.
- Recover the effective denominator and new paper length.
- Check the unchanged represented real length.
A straight feature is 7.5 cm on a 1:240 scale drawing. Find its real length and its required drawing length at 1:150.
Give me a hint
Recover the real length in one unit before applying the second scale.
Compare my reasoning
- Recover the real length using the original scale: 7.5×240=1800 cm=18 m.
- Keep that same real feature when changing the drawing scale; only the representation changes.
- At 1:150, the required drawing length is 1800÷150=12 cm.
- Check both representations: 7.5×240=12×150=1800 cm. These exact stated lengths do not certify an actual ruler reading.
The real feature is 18 m long, and its required length at 1:150 is 12 cm.
Look for these in your work
- Use the original scale to recover a real length.
- Use that same feature in the new scale.
- Check both drawing-to-real products.
Common mistakes
- Assuming the smaller scale denominator gives the smaller drawing.
- Keeping an old numerical scale legend after enlarging the printed copy.
- Applying a squared scale to a door width or wall length.
What can you explain now?
A 1:120 plan is printed at 200% of its original linear size. What effective scale applies to the new copy?
Compare with the explanation
1:60.
The linear print multiplier is 2, so the new denominator is 120÷2=60. The old 1:120 label would no longer describe lengths measured on the enlarged copy.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
What stays fixed when a plan is resized, and how do you check whether its printed scale label still applies?
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.