How do I tell corresponding, alternate and co-interior angles apart?

Look at the two angles relative to the transversal: same side and same position gives corresponding angles, opposite sides inside the parallels gives alternate angles, same side inside gives co-interior angles.

Must the degree symbol be written in the answer?

Yes. Always give the unit with the size of an angle or marks are lost for the final answer.

S1 Maths: Angles and Parallel Lines, Paper 3 (Challenge)

2026-11-09

Tutor Prep Guide · S1 Maths

Ten challenge items mixing angle ratios, two-step equations and all three parallel-line angle relations, with full answers and explanations.

Can one figure contain several angle relations?　Yes. A single figure often mixes vertically opposite, corresponding and co-interior angles, so each angle must be judged separately.

01　Paper details (check answers afterwards)

Item	Detail
Questions	10
Suggested time	25
Difficulty mix	Foundation 3 · Intermediate 2 · Challenge 4 · Error redo 1
Chapter	Chapter: S1 Maths: Angles and Parallel Lines
Level	Level: Challenge

02　Questions (10 items)

FoundationThree angles meet at a point and are in the ratio 2 : 3 : 4. Find the three angles.
FoundationTwo parallel lines are cut by a transversal. A pair of co-interior angles is 3x − 20 and 2x + 30. Find x and the angles.
IntermediateTwo lines intersect. A pair of vertically opposite angles is 7x − 5 and 4x + 40. Find the angle and its supplement.
IntermediateTwo parallel lines are cut by a transversal. A pair of co-interior angles is 2x + 15 and 3x + 35. Find x and the angles.
FoundationFour angles meet at a point: 85°, 95°, 110° and x. Find x.
ChallengeAn angle and its supplement are in the ratio 5 : 7. Find the two angles.
ChallengeA transversal cuts two parallel lines. A pair of alternate angles is 4x + 10 and 6x − 30. Find the angle and its co-interior angle.
ChallengeThree angles 2x + 20, 3x − 10 and 60° lie on a straight line. Find x and the angles.
ChallengeA transversal cuts two parallel lines and one angle is 118°. Find its alternate angle, its co-interior angle and the difference.
Error redoA student treats corresponding angles as supplementary. Given one corresponding angle of 132°, find the other and give the correct reason.

03　Answers and one-line notes

#	Answer	One-line note
1	The angles are 80°, 120° and 160°	Divide 360° into 9 equal parts of 40°.
2	x = 34, the angles are 82° and 98°	Solve 5x + 10 = 180 because co-interior angles are supplementary.
3	The angle is 100° and its supplement is 80°	Use 7x − 5 = 4x + 40 to get x = 15, then take the supplement.
4	x = 26, the angles are 67° and 113°	Solve 5x + 50 = 180 because co-interior angles are supplementary.
5	x = 70°	Angles at a point add up to 360°.
6	The angles are 75° and 105°	The two angles add up to 180°; split it in the ratio 5 : 7.
7	The angle is 90° and its co-interior angle is 90°	Alternate angles give x = 20 and an angle of 90°, so the co-interior angle is also 90°.
8	x = 22, the angles are 64°, 56° and 60°	Adjacent angles on a straight line add up to 180, so 5x + 70 = 180.
9	Alternate angle 118°, co-interior angle 62°, difference 56°	The alternate angle is equal and the co-interior angle is supplementary, so they differ by 56°.
10	The other is 132°; corresponding angles are equal	Corresponding angles are equal; it is co-interior angles that add up to 180.

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.