The ratio of half-lives for a reaction with starting B of 0.05 M and 0.01 M can be calculated using the formula t1/2 = (0.693/k), where t1/2 is the half-life and k is the rate constant.
The rate constant can be determined by the equation k = ln(2) / t1/2. Given that the concentrations are different, the rate constant will also be different for each concentration.
Therefore, the ratio of half-lives will depend on the specific reaction and the rate constants associated with each concentration. To provide a more accurate answer, please provide the specific rate constant values for each concentration.