Three bells toll at intervals of 9,12 and 15 minutes respectively

Three bells toll at intervals of 9,12 and 15 minutes respectively. All the three begin to toll at 9 a.m. At what time will they again toll together?
(a) 11.30 a.m.
(b) 11.45 a.m.
(c) 12.00 noon
(d) 11.20 a.m.

Anurag Mishra Professor Asked on 4th May 2016 in Maths.
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  • 1 Answer(s)

    Answer: (c) 12.00 noon 

    Solution:-
    The factors of 9 = 3 x 3 
    The factors of 12 = 2 x 2 x 3
    The factors of 15 = 3 x 5

    Then, the L C M of 9, 12 and 15 = 2 x 2 x 3 x 3 x 5
     = 180

    So, after 180 minutes the bell toll together.
    Then, time will be 9 a. m. + 180/60 hours 
     = 9 a. m. + 3 hours
    = 12 noon.

    Hence, the correct answer is option (c) 12.00 noon.  

    Anurag Mishra Professor Answered on 4th May 2016.
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