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The probability of guessing the… (Class 10 Maths 2025, Q22)

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MathsCBSE Class 10 · Standard · Board exam 2025, set 30/3/1 · 2 marks · Very short answer

CBSE Class 10 Mathematics Standard 2025: question 22

Set in the CBSE Class 10 board exam of 2025, paper 30/3/1, section B, question 22, for 2 marks. Try it first; the hints and our step-by-step solution are below.

Q22 · 2 marks · Very short answerProbability

The probability of guessing the correct answer of a certain test question is . If the probability of not guessing the correct answer is , then find the value of x.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2025 board paper, set 30/3/1.

Hints

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

Hint 1

How are the probability of an event and the probability of it not happening related?

Hint 2

Their sum is 1. Set up an equation in x.

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. Guessing correctly and not guessing correctly are complementary events, so :

    1 mark

  2. , so

    1 mark

Answer:

Where the marks are

  • Writes using complementary events (1 mark)
  • Solves to get (1 mark)

Revise the chapter

Practise this chapterBoard-style questions from Probability, one at a time, marked against the answer key and marking points.Back to the full paper2025 board paper, set 30/3/1 (Standard): 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.