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Assertion (A) : All… (Class 10 Maths Basic 2025, Q20)

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MathsCBSE Class 10 · Basic · Board exam 2025, set 430/2/1 · 1 mark · Assertion-reason

CBSE Class 10 Mathematics Basic 2025: question 20

Set in the CBSE Class 10 board exam of 2025, paper 430/2/1, section A, question 20, for 1 mark. Try it first; the hints and our step-by-step solution are below.

Q20 · 1 mark · Assertion-reasonCompetency-basedTriangles

Assertion (A) : All congruent triangles are similar. Reason (R) : In congruent triangles, the ratio of corresponding sides is 1 : 1. Codes: (A) Both A and R are true and R is the correct explanation of A. (B) Both A and R are true, but R is not the correct explanation of A. (C) A is true, but R is false. (D) A is false, but R is true.

  1. (A)Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
  2. (B)Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
  3. (C)Assertion (A) is true, but Reason (R) is false.
  4. (D)Assertion (A) is false, but Reason (R) is true.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2025 board paper, set 430/2/1.

Hints

Open one hint at a time and try again before the next.

Hint 1

What are the conditions for two triangles to be similar?

Hint 2

Is a ratio of 1 : 1 still a proportion?

Step-by-step solution

Each step shows the marks it earns, as an examiner would award them. Checked by an independent re-solve from the question paper.

  1. Congruent triangles have equal corresponding angles and their corresponding sides are in the ratio 1 : 1, so R is true.

  2. Sides in proportion (ratio 1 : 1) satisfy the condition for similarity, so A is true and R explains it. The answer is option (A).

    1 mark

Answer: Option (A)

Where the marks are

  • Recognises both are true and R explains A (1 mark)

Revise the chapter

  • Chapter: Triangles (notes, formulas, where marks are lost and every past question)
Practise this chapterBoard-style questions from Triangles, one at a time, marked against the answer key and marking points.Back to the full paper2025 board paper, set 430/2/1 (Basic): every question, by section.

The question is transcribed from the official paper; figures are described in words. The solution, hints and chapter tag are ours. Spotted an error? Write tosupport@questionbuddy.in.