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7th Class Mathematics Integers Question Bank Number System

  • question_answer
    The bells begin tolling at the same time and continued to do so at intervals of 21, 28, 30 seconds respectively. The bells will toll together again after

    A) 7 seconds        

    B) 420 seconds

    C) 630 seconds   

    D) 1764 seconds

    Correct Answer: B

    Solution :

    The time after which they will toll together again must be a multiple of 21, 28 and 30. Hence LCM of 21, 28 and 30 is 420.


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