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 2 (Intermediate)

2026-11-09

Tutor Prep Guide · S1 Maths

Ten intermediate items that write angles as algebraic expressions and form equations, plus angles at a point and ratio questions, each with an answer and a short explanation.

Can angles be found with equations?　Yes. Decide whether the pair is equal or supplementary, write the equation, solve for x, then substitute back to check the sum.

01　Paper details (check answers afterwards)

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

02　Questions (10 items)

FoundationOn a straight line, two equal angles together with an angle of 38° form the straight line. Find each equal angle.
Foundation2x and 3x are complementary. Find x and the two angles.
FoundationFind the supplement of 63° and the complement of 24°.
IntermediateTwo lines intersect. A pair of vertically opposite angles is 5x − 10 and 3x + 20. Find x and the angle.
IntermediateA transversal cuts two parallel lines. A pair of alternate angles is 4x − 15 and 2x + 25. Find x and the angle.
IntermediateTwo parallel lines are cut by a transversal. A pair of co-interior angles is 3x + 10 and 2x. Find x and the two angles.
ChallengeA transversal cuts two parallel lines and one corresponding angle is 118°. Find the co-interior angle on the same side.
ChallengeFour angles meet at a point. Two of them are 65° each and another is 90°. Find the fourth angle.
ChallengeA transversal cuts two parallel lines. A pair of co-interior angles is in the ratio 4 : 5. Find the angles and the corresponding angle of the larger one.
Error redoA student adds a pair of alternate angles to 180°. Given one alternate angle of 74°, find the other and give the correct reason.

03　Answers and one-line notes

#	Answer	One-line note
1	Each angle is 71°	Subtract 38° from 180° and halve.
2	x = 18, the angles are 36° and 54°	Complementary angles add up to 90°.
3	Supplement 117°, complement 66°	Supplementary angles add up to 180 and complementary angles add up to 90; do not mix them up.
4	x = 15, the angle is 65°	Solve 5x − 10 = 3x + 20 because vertically opposite angles are equal.
5	x = 20, the angle is 65°	Solve 4x − 15 = 2x + 25 because alternate angles are equal.
6	x = 34, the angles are 112° and 68°	Solve 3x + 10 + 2x = 180 as co-interior angles are supplementary.
7	The co-interior angle is 62°	The corresponding angle equals 118°, so the co-interior angle is 180° − 118°.
8	The fourth angle is 140°	Angles at a point add up to 360°.
9	The angles are 80° and 100°; the corresponding angle of the larger one is 100°	Split 180° in the ratio 4 : 5; corresponding angles equal the larger angle.
10	The other is 74°; alternate angles are equal, not supplementary	Alternate angles between parallel lines 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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