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HCF & LCM · Question 31 of 63

Question 31

EasyOriginal question

Three temple bells ring at intervals of 9, 12 and 15 minutes. They ring together at 8:00 am. When will they next ring together?

Options for question 31

Show the answer and explanation
CorrectNot quiteAnswer A

Correct answer: A

Explanation

  1. They ring together again after LCM(9, 12, 15) minutes.

  2. LCM = 22×32×5=1802^2 \times 3^2 \times 5 = 180 minutes = 3 hours.

  3. 8:00 am + 3 hours = 11:00 am.

Worth noting

8:36 am, 8:45 am and 9:00 am are the LCMs of only two of the bells (36, 45 and 60 minutes).

Concept
LCM for events repeating together
Typical time
40 s
Your time
—
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