Lines and Angles — Class 9 MCQs with Answers
Class 9 CBSE Mathematics · Chapter 11
90 practice questions · 30 Easy · 30 Medium · 30 Hard · Updated
Practise the most important Class 9 CBSE Mathematics questions from Chapter 11, "Lines and Angles". You get 9 timed quizzes made from 90 NCERT-based MCQs, with answers and explanations. The questions are split into 30 Easy, 30 Medium and 30 Hard. Warm up on the basics, then move on to the exam-level questions that set top scorers in CBSE Board exams and the JEE & NEET foundation years apart.
To score well in "Lines and Angles", focus on fast problem-solving, formula recall and step-by-step working. Each MCQ here is timed and uses exam-style marking (+4 correct, −1 wrong, 0 skipped). This trains you to stay accurate under time pressure, as real papers need. Every question has a short explanation, so a wrong answer becomes a quick lesson. It is the fastest way to fix gaps before a test.
Use this chapter for focused revision. Start with the Easy set to check your basics on Lines and Angles, then move to Medium and Hard to practise applying them. Your accuracy, streaks and XP save automatically. This chapter also adds to your overall Class 9 Mathematics mastery score. 14 sample questions are solved in full below, with the answer and a worked explanation. Sign in free to start practising.
Key concepts: Lines and Angles (Class 9 Mathematics)
When two lines meet they form angles with fixed relationships, and when a transversal cuts parallel lines those relationships multiply. This chapter establishes the linear pair and vertically opposite angle results, the parallel-line angle pairs, and the angle sum of a triangle.
- Line, ray and line segment
- A line extends endlessly in both directions, a ray in one, and a segment has two endpoints and a definite length.
- Types of angles
- Acute below 90°, right exactly 90°, obtuse between 90° and 180°, straight exactly 180°, and reflex beyond 180°.
- Complementary and supplementary angles
- Two angles adding to 90° are complementary; two adding to 180° are supplementary.
- Adjacent angles
- Angles sharing a common vertex and a common arm, with no overlap between their interiors.
Lines and Angles — important questions & MCQs with answers (Class 9 Mathematics)
14 solved questions from this chapter's difficulty levels, each with its answer and explanation. The other 76 are timed and scored when you sign in.
- Q1Easy
An angle less than 90° is called:
A.ObtuseB.Acute✓ CorrectC.RightD.ReflexAnswer: B. Acute
Explanation: An acute angle lies strictly between 0° and 90°. A 90° angle is right, and anything above 90° up to 180° is obtuse, not acute.
- Q2Easy
Two angles whose sum is 90° are called:
A.Complementary angles✓ CorrectB.Supplementary anglesC.Vertically opposite anglesD.Linear pairAnswer: A. Complementary angles
Explanation: Complementary angles add to 90°, e.g. 30°+60°=90°. Supplementary angles add to 180° instead — a common mix-up between the two rules.
- Q3Easy
When a transversal cuts two parallel lines, corresponding angles are:
A.SupplementaryB.ComplementaryC.Equal✓ CorrectD.Right anglesAnswer: C. Equal
Explanation: Corresponding angles sit in matching positions at each parallel line crossing and are equal when the lines are parallel — not supplementary, which is the co-interior rule.
- Q4Easy
The sum of all angles of a triangle is:
A.90°B.180°✓ CorrectC.270°D.360°Answer: B. 180°
Explanation: The angle sum property states every triangle's three interior angles add to exactly 180°, whatever the triangle's shape or size.
- Q5Easy
An angle equal to 90° is called a:
A.Right angle✓ CorrectB.Obtuse angleC.Reflex angleD.Straight angleAnswer: A. Right angle
Explanation: A right angle measures exactly 90°, no more and no less — 91° would already count as obtuse, not right.
- Q6Easy
The supplement of 65° is:
A.25°B.125°C.295°D.115°✓ CorrectAnswer: D. 115°
Explanation: The supplement of an angle is 180° minus the angle: 180°−65°=115°. Do not confuse this with the complement (90°−65°=25°), a different pair.
- Q7Medium
A ray OC bisects angle AOB = 80°. Find angle AOC.
A.80°B.20°C.40°✓ CorrectD.160°Answer: C. 40°
Explanation: A bisector splits an angle into two equal halves, so ∠AOC=80°÷2=40°. Using the full 80° instead of halving it is the common slip.
- Q8Medium
Two supplementary angles are in ratio 2:3. Find the larger angle.
A.90°B.72°C.108°✓ CorrectD.120°Answer: C. 108°
Explanation: Let the angles be 2x and 3x; being supplementary, 2x+3x=180° gives x=36°. The larger angle is 3×36°=108°, not the smaller one, 2×36°=72°.
- Q9Medium
If l ∥ m and a transversal makes an angle of 55° with l, find the alternate interior angle with m.
A.125°B.55°✓ CorrectC.35°D.90°Answer: B. 55°
Explanation: Alternate interior angles are equal when the lines are parallel, so the angle at m is also 55° — it is not the co-interior angle, which would instead be 180°−55°=125°.
- Q10Medium
Two angles of a triangle are 65° and 75°. Find the third angle.
A.40°✓ CorrectB.50°C.60°D.30°Answer: A. 40°
Explanation: By the angle sum property, the third angle is 180°−65°−75°=40°. Adding all three given numbers instead of subtracting from 180° is the usual error.
- Q11Medium
Two lines intersect and one angle is 70°. Find all four angles.
A.70°,120°,70°,100°B.70°,70°,70°,70°C.90°,90°,90°,90°D.70°,110°,70°,110°✓ CorrectAnswer: D. 70°,110°,70°,110°
Explanation: Vertically opposite angles are equal, so the 70° angle repeats directly across the point. Each neighbouring angle forms a linear pair with it: 180°−70°=110°, giving 70°,110°,70°,110° around the point.
- Q12Hard
Two lines intersect at O. OA and OB are rays such that angle AOB = (5x+10)° and its vertically opposite angle is (3x+50)°. Find x and the angle.
A.x=25, angle=115°B.x=20, angle=110°✓ CorrectC.x=20, angle=120°D.x=15, angle=85°Answer: B. x=20, angle=110°
Explanation: Vertically opposite angles are equal: 5x+10=3x+50 gives 2x=40, so x=20°. The angle is 5(20°)+10°=110°, matching 3(20°)+50°=110° as a check.
- Q13Hard
AB ∥ CD. A transversal cuts them. If one alternate interior angle is (3x−10)° and the other is (2x+15)°, find x.
A.35B.30C.20D.25✓ CorrectAnswer: D. 25
Explanation: Alternate interior angles are equal when AB∥CD: 3x−10=2x+15, so x=25. Setting the two expressions supplementary instead of equal is the usual mistake for this angle pair.
- Q14Hard
In ΔABC, the exterior angle at B is twice the interior angle at A. If angle C = 50°, find angle A.
A.50°✓ CorrectB.65°C.40°D.80°Answer: A. 50°
Explanation: The exterior angle at B equals the sum of the two remote interior angles, ∠A+∠C. Since it also equals 2∠A, then 2∠A=∠A+50° gives ∠A=50°.
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Start this chapter free →Lines and Angles — FAQs
What are the key concepts in Class 9 Mathematics Lines and Angles?+
When two lines meet they form angles with fixed relationships, and when a transversal cuts parallel lines those relationships multiply. This chapter establishes the linear pair and vertically opposite angle results, the parallel-line angle pairs, and the angle sum of a triangle. Key ideas include Line, ray and line segment, Types of angles, Complementary and supplementary angles, Adjacent angles.
What does Class 9 Mathematics Chapter 11 (Lines and Angles) cover on XamBaaz?+
It has 90 NCERT-based MCQs on "Lines and Angles": 30 Easy, 30 Medium and 30 Hard. Together they make 9 timed quizzes, and you never get the same set twice. Every question has an instant explanation. They help you prepare for CBSE Board exams and the JEE & NEET foundation years.
Are these "Lines and Angles" questions free to practise?+
Yes. Sign in with Google to practise "Lines and Angles" free. Full unlimited access is ₹999/year on a launch offer until 1 December 2026. No chapter is charged separately.
How should I revise "Lines and Angles" for the exam?+
Start with the Easy quiz to check your basics, then try Medium and Hard to practise applying them. There are 9 timed quizzes on this chapter, so you can come back for a fresh set instead of one you have seen. Read each explanation, retry the questions you miss, and track your accuracy until it stays high.
Are these "Lines and Angles" MCQs available with answers?+
Yes. 14 sample questions are shown here in full, each with the correct option and a step-by-step "Why" explanation. Sign in free with Google to start practising, with instant scoring.
Is there negative marking in the "Lines and Angles" quizzes?+
Yes. The timed quizzes use exam-style marking: +4 for a right answer, −1 for a wrong one and 0 for a skip. MHT-CET and CBSE board papers have no negative marking. Our mocks for those are scored their way.
What are the important questions from Lines and Angles (Class 9 Mathematics)?+
The questions that matter most test Line, ray and line segment, Types of angles, Complementary and supplementary angles, Adjacent angles. This page shows 14 solved important MCQs with answers and explanations; all 90 questions on the chapter are available as timed quizzes once you sign in.
Is there an online quiz for Lines and Angles?+
Yes — Class 9 Mathematics Lines and Angles has timed online quizzes at Easy, Medium and Hard levels, with instant scoring and a worked explanation on every question. The first quiz on the chapter is free.