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Question

# Samaira heard 3 bells toll together at 10:00 AM. The first bell tolls after every 5 second, the second tolls after every 9 seconds and the third tolls after every 10 seconds. When will they toll together again?

A
After 45 seconds
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B
After 3 minutes
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C
After 2 minutes and 30 seconds
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D
After 90 seconds
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Solution

## The correct option is D After 90 secondsThe bells will ring together at common times. And this time will be a multiple of all the times at which the 3 bells ring individually, that is 5, 9 and 10. We have to find the LCM (least common multiple) of these numbers to know after what time all the 3 bells toll together. ∴LCM of 5, 9, 10=5×2×3×3 = 90 So the bells will together after every 90 seconds.

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