Use the change of base formula to compute $\log _{1 / 5} 8$. Round your answer to the nearest thousandth.

Step 1 ：Use the change of base formula to compute \(\log _{1 / 5} 8\). The change of base formula is given by \(\log_b a = \frac{\log_c a}{\log_c b}\) for any positive base c ≠ 1.

Step 2 ：We can use this formula to compute \(\log _{1 / 5} 8\) by choosing c to be 10 (the common logarithm) or e (the natural logarithm). The result should be the same regardless of the base we choose.

Step 3 ：The results from both the base 10 and natural logarithm calculations are the same, as expected. This confirms that the change of base formula works correctly.

Step 4 ：The result is a negative number because 8 is less than 1/5, so the logarithm base 1/5 of 8 is negative.

Step 5 ：Final Answer: The value of \(\log _{1 / 5} 8\) rounded to the nearest thousandth is \(\boxed{-1.292}\).