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A bag contains 40… (Class 10 Maths Basic 2025, Q24a)

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MathsCBSE Class 10 · Basic · Board exam 2025, set 430/5/1 · 2 marks · Very short answer

CBSE Class 10 Mathematics Basic 2025: question 24(a)

Set in the CBSE Class 10 board exam of 2025, paper 430/5/1, section B, question 24(a), for 2 marks. Try it first; the hints and our step-by-step solution are below.

Q24(a) · 2 marks · Very short answerProbability

A bag contains 40 marbles out of which some are white and others are black. If the probability of drawing a black marble is , then find the number of white marbles.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2025 board paper, set 430/5/1.

Hints

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

Hint 1

Probability = favourable outcomes ÷ total outcomes. Let the black marbles be .

Hint 2

Solve , then subtract from the total.

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. Let the number of black marbles be . Then P(black) .

    ½ mark

  2. 1 mark

  3. Number of white marbles

    ½ mark

Answer: 16 white marbles

Where the marks are

  • Writes P(black) (½ mark)
  • Equates to and gets 24 black marbles (1 mark)
  • Finds white marbles = 16 (½ 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 430/5/1 (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.