How often should an error be redone?

Until you can name the wrong step out loud; redo it a day later and two correct answers in a row means it is fixed.

Perimeter uses cm and area uses cm², so a wrong unit usually means the wrong formula was chosen.

P1 Maths: 2D Shapes (10 Error-Correction Items)

2026-11-08

Ten error-correction items: fixing the ideas that a rectangle has four equal sides, that a perimeter is an area, and that a square perimeter is a side times two, plus cutting corners, joining shapes and equal perimeters with different areas.

Focus　Name the wrong step first, then work the question again and always give the unit.

01　Paper details (check answers afterwards)

Item	Detail
Questions	10
Suggested time	25
Difficulty mix	Foundation 2 · Intermediate 3 · Challenge 3 · Error redo 2
Chapter	Chapter: P1 Maths: 2D Shapes
Level	P1 Maths

02　Questions (10 items)

FoundationA student writes that all four sides of a rectangle are the same length. What is wrong, and what is correct?
FoundationA triangle has sides of 4 cm, 4 cm and 5 cm. What is its perimeter?
IntermediateA square has 6 cm sides; a rectangle is 8 cm by 3 cm. Which perimeter is longer, and by how much?
IntermediateHow many 1 cm matches are needed to make a square with 5 cm sides?
IntermediateA hexagon has one corner cut off. How many sides does the new shape have?
ChallengeA student says a circle has two edges, one outer and one inner. What is correct?
ChallengeTwo identical equilateral triangles with 5 cm sides are joined to make a rhombus. What is its perimeter?
ChallengeA 8 cm by 2 cm rectangle and a 5 cm square both have a perimeter of 20 cm. How much do their areas differ?
Error redoA student answers 28 cm² for the perimeter of a 7 cm by 4 cm rectangle. What went wrong, and what is correct?
Error redoA student uses one side times two and answers 16 cm for a square with 8 cm sides. What is wrong, and what is correct?

03　Answers and one-line notes

#	Answer	One-line note
1	Only opposite sides of a rectangle are equal; all four sides are equal in a square.	Tell them apart by the sides: opposite sides equal means a rectangle; four equal sides means a square.
2	4 + 4 + 5 = 13 cm.	The perimeter of a triangle is the sum of its three sides, not one side times three.
3	Square 6 × 4 = 24 cm; rectangle (8 + 3) × 2 = 22 cm; the square is 2 cm longer.	Work out both perimeters before comparing; a single side proves nothing.
4	5 × 4 = 20, so 20 matches.	The four sides are equal, so the number of matches equals the perimeter in centimetres.
5	6 − 1 + 2 = 7, so it becomes a heptagon.	Cutting one corner removes a vertex and adds two, a net gain of one side.
6	A circle has one continuous curved edge closed on itself, and no corners.	A circle is enclosed by one closed curve, so it has a single edge.
7	The rhombus has four sides of 5 cm, so the perimeter is 5 × 4 = 20 cm.	The two touching sides are hidden and do not count in the perimeter.
8	Rectangle 8 × 2 = 16 cm², square 5 × 5 = 25 cm², a difference of 9 cm².	Equal perimeters do not give equal areas, so both areas must be worked out.
9	The two sides were multiplied, which gives the area; the perimeter is (7 + 4) × 2 = 22 cm.	Perimeter is the distance around and is measured in cm; area uses cm².
10	Only two sides were counted; a square has four equal sides, so the perimeter is 8 × 4 = 32 cm.	Multiply a square by four; only a rectangle uses length plus width doubled.

04　What to do after marking

After marking, redo only the wrong items and write down which step went wrong (formula, unit, or misread number).
Repeat the same item two days later; move to the next paper only when both attempts are correct.
Parents only need the answer and note columns; there is no need to explain every item.

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Questions and answers are written originally by the TutorZone team and are not taken from any school, publisher or examination authority paper. Every value is checked by computer.