The Taylor’s tool life index is

Question

.        In a tool life test doubling the cutting speed reduce the tool life to  $\frac{1}{8}$ th  of the orginal. The Taylor’s tool life index is  

(a) $\frac{1}{2}$                           (b) $\frac{1}{3}$

(c) $\frac{1}{4}$                             (d) $\frac{1}{8}$