The ratio of its torque carrying capacity to that of a solid shaft of the same material and the same outside diameter is

Question

The outside diameter of a hollow shaft is twice its inside diameter the ratio of its torque carrying capacity to that of a solid shaft of the same material and the same outside diameter is                                                          

      (a) 15/16                                                             (b) 3/4

      (c) 1/2                                                                 (d) 1/16