How should error-review items be done?

Redo them unaided, then check; two fully correct papers in a row means the item is mastered.

Why can a triangle have at most one right angle?

Two right angles already use 180°, leaving 0° for the third angle.

When can three lengths form a triangle?

Any two sides must add to more than the third; equal is not enough.

P4 Maths Classifying Triangles Paper 4: Error Review

2026-11-09

Tutor Prep Guide · P4 Maths

Ten original items, each with an answer and a one-line explanation.

Direct answers　Items 1-3 are basic, 4-6 intermediate and 7-9 challenge, with item 10 as the error review. Time yourself first, then check each answer and redo what is wrong.

01　Paper details (check answers afterwards)

Item	Detail
Questions	10
Suggested time	20
Difficulty mix	Foundation 3 · Intermediate 3 · Challenge 3 · Error redo 1
Chapter	Chapter: P4 Maths Classifying Triangles
Level	P4

02　Questions (10 items)

FoundationError review: what do the three angles of a triangle add up to?
FoundationTwo angles of a triangle are 60° each. Find the third angle and name the triangle.
FoundationA triangle has sides 6 cm, 6 cm and 9 cm. How is it classified by its sides?
IntermediateAn isosceles triangle has an apex angle of 40°. What is each base angle?
IntermediateOne acute angle of a right-angled triangle is 35°. What is the other acute angle?
IntermediateA triangle has angles 50°, 60° and 70°. How is it classified by its angles?
ChallengeAn isosceles triangle has base angles of 75°. Find the apex angle and classify it by its angles.
ChallengeCan three sticks of 7 cm, 7 cm and 14 cm form a triangle?
ChallengeOne angle of a triangle is twice another, and the third angle is 90°. What is the smallest angle?
Error redoError review: a pupil says a triangle can have two right angles. Is that right?

03　Answers and one-line notes

#	Answer	One-line note
1	180 degrees	The angle sum of a triangle is 180 degrees; 360 degrees is for a quadrilateral.
2	60 degrees, an equilateral triangle	180 minus 60 minus 60 = 60 degrees, so all angles are 60° and it is equilateral.
3	An isosceles triangle	Only two sides are equal, so it is isosceles, not equilateral.
4	70 degrees	(180 minus 40) divided by 2 = 70 degrees, since the two base angles are equal.
5	55 degrees	180 minus 90 minus 35 = 55 degrees, so the other acute angle is 55 degrees.
6	An acute-angled triangle	All three angles are below 90°, so it is acute-angled.
7	30 degrees, an acute-angled triangle	180 minus 75 times 2 = 30 degrees; 30, 75 and 75 are all below 90°, so it is acute-angled.
8	No	7 plus 7 equals 14, not greater than the third side, so the three lengths cannot close a triangle.
9	30 degrees	Let the smallest be x: x plus 2x plus 90 = 180, so 3x = 90 and x = 30 degrees.
10	No	Two right angles already make 90 plus 90 = 180 degrees, leaving 0 for the third, so a triangle has at most one right angle.

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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