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Two alarm clocks ring… (Class 10 Maths Basic 2024, Q26)

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MathsCBSE Class 10 · Basic · Board exam 2024, set 430/1/1 · 3 marks · Short answer

CBSE Class 10 Mathematics Basic 2024: question 26

Set in the CBSE Class 10 board exam of 2024, paper 430/1/1, section C, question 26, for 3 marks. Try it first; the hints and our step-by-step solution are below.

Q26 · 3 marks · Short answerReal Numbers

Two alarm clocks ring their alarms at regular intervals of 20 minutes and 25 minutes respectively. If they first beep together at 12 noon, at what time will they beep again together next time ?

Source: official question paper from cbse.gov.in (PDF). See it in the full 2024 board paper, set 430/1/1.

Hints

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

Hint 1

The clocks beep together at times that are common multiples of 20 and 25.

Hint 2

Find the LCM using prime factorisation, then add that time to 12 noon.

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. They beep together again after LCM(20, 25) minutes. , , so LCM minutes.

    2 marks

  2. 100 minutes = 1 hour 40 minutes. So next time together = 12:00 noon + 1 h 40 min = 1:40 pm.

    1 mark

Answer: 1:40 pm

Where the marks are

  • Finds LCM(20, 25) = 100 (2 marks)
  • Converts to 1 h 40 min and states 1:40 pm (1 mark)

Revise the chapter

Practise this chapterBoard-style questions from Real Numbers, one at a time, marked against the answer key and marking points.Back to the full paper2024 board paper, set 430/1/1 (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.