skgmatclub2016 wrote:

In a courtyard, one bell rings every 1/4 hour and another bell rings every 1/5 hour. Both bells ring together at exactly the beginning of each hour. Which of the following gives all the intervals that occur between any two rings of the bells in minutes ?

A. 6 and 9 only

B. 3, 6 and 9

C. 3, 12 and 15

D. 3, 6, 9 and 12

E. 3, 6, 10 and 12

For every 4th of an hour, bell one rings on minutes 15, 30, 45, and 60.

For every 5th of an hour, bell two rings on minutes 12, 24, 36, 48, and 60.

Since 15 - 12 = 3, 30 - 24 = 6, 45 - 36 = 9 and 60 - 48 = 12, the intervals are 3, 6, 9 and 12.

Answer: D

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