Bell A rings every 5 minutes and bell B rings every 6 minutes. If the two bells rang at 7:00 AM, then at what time will they ring together again? ( 3 marks)

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Solution

To find the number of minutes after which the 2 bells would ring together, we need to find the LCM of 5 and 6. (0.5 mark)
Multiples of 5: 5, 10, 15, 20, 25, 30,... (0.5 mark)
Multiples of 6: 6, 12, 18, 24, 30,... (0.5 mark)
Thus, the LCM of 5 and 6 = 30. (0.5 mark)
So, the next time they will ring together will be 30 minutes after 7:00 AM, which would be 7:30 AM.(1 mark)

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