How is classifying by angles different from by sides?

By angles you look at the largest angle; by sides you count how many sides are equal.

How do isosceles and equilateral triangles relate?

Every equilateral triangle is also isosceles, but not every isosceles triangle is equilateral.

Why is the angle sum 180°?

At P4 you just use the result: subtract the two known angles from 180° to find the third.

P4 Maths Classifying Triangles Paper 2: Intermediate

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)

FoundationAn isosceles triangle has an apex angle of 40°. What is each base angle?
FoundationOne base angle of an isosceles triangle is 65°. What is the apex angle?
FoundationTwo angles are 35° and 55°. Find the third angle and classify the triangle by its angles.
IntermediateAn equilateral triangle has a perimeter of 36 cm. How long is each side?
IntermediateAn isosceles triangle has perimeter 30 cm and each equal side is 11 cm. How long is the base?
IntermediateTwo angles are 100° and 40°. Find the third angle and classify the triangle by its angles.
ChallengeOne acute angle of a right-angled triangle is 25°. What is the other acute angle?
ChallengeThe largest angle of a triangle is 100° and the other two are equal. What is each?
ChallengeAn isosceles triangle has an apex angle of 90°. Find each base angle and name the triangle.
Error redoError review: a pupil used 360° as the angle sum and answered 210° for angles 80° and 70°. What is correct?

03　Answers and one-line notes

#	Answer	One-line note
1	70 degrees	The two base angles are equal, so (180 minus 40) divided by 2 = 70 degrees.
2	50 degrees	The two base angles take 65 times 2 = 130°, so 180 minus 130 = 50 degrees.
3	90 degrees, a right-angled triangle	180 minus 35 minus 55 = 90 degrees, exactly a right angle.
4	12 cm	All three sides are equal, so 36 divided by 3 = 12 cm.
5	8 cm	The two equal sides take 11 times 2 = 22 cm, so the base is 30 minus 22 = 8 cm.
6	40 degrees, an obtuse-angled triangle	180 minus 100 minus 40 = 40 degrees; the largest angle 100° is above 90°, so it is obtuse-angled (and isosceles).
7	65 degrees	The two acute angles add to 90°, so 90 minus 25 = 65 degrees.
8	40 degrees	The other two take 180 minus 100 = 80°, so each is 80 divided by 2 = 40 degrees.
9	45 degrees each, an isosceles right-angled triangle	(180 minus 90) divided by 2 = 45 degrees; a right angle plus two equal sides gives an isosceles right-angled triangle.
10	30 degrees	The angle sum of a triangle is 180°, so 180 minus 80 minus 70 = 30 degrees.

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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