10th Class Mathematics Real Numbers Question Bank Real Numbers

  • question_answer Four different electronic devices make a beep after every 30 minutes, 1 hour, \[1\frac{1}{2}\]hour and 1 hour 45 minutes respectively. All the devices beeped together at 12 noon. They will again beep together at _____.       

    A) 12 midnight   

    B) 3a.m.                          

    C)  6a.m.             

    D)         9a.m.

    Correct Answer: D

    Solution :

    L.C.M. \[(30,\,\,60,\,\,90,\,105)={{2}^{2}}\times {{3}^{2}}\times 5\times 7\]' = 1260 mins = 21 hours

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