Three bells ring at intervals of 4, 7 and 14 minutes. All three rang at 6 AM. When will they ring together again?

(a) 6:07 AM   (b) 6:14 AM   (c) 6:28 AM   (d) 6:25 AM

This question is inspired from Question 21 - CBSE Sample Papers (2021 Boards) - Maths Standard

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Transcript

Question 30 Three bells ring at intervals of 4, 7 and 14 minutes. All three rang at 6 AM. When will they ring together again? (a) 6:07 AM (b) 6:14 AM (c) 6:28 AM (d) 6:25 AM Let the bells ring at 1, 2, 3 minutes At 6 minutes, all of them ring together. Now, this 6 is actually the LCM of 1, 2, 3 So, Time when they ring together = LCM of 1, 2, 3 Here, Time when they next ring together = LCM of 4, 7 and 14 Finding LCM Thus, LCM = 2 × 2 × 7 = 28 Thus, the three bells ring together after 28 minutes Hence, Time when the three bells ring together is 6:28 am So, the correct answer is (c)

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Davneet Singh has done his B.Tech from Indian Institute of Technology, Kanpur. He has been teaching from the past 13 years. He provides courses for Maths, Science, Social Science, Physics, Chemistry, Computer Science at Teachoo.