Solution
= Solution
For independent <exponential distributions>, the numerator from part a(ii) is
$$
\int_0^c\lambda_1e^{-(\lambda_1+\lambda_2)t}\,dt
=\frac{\lambda_1}{\lambda_1+\lambda_2}
\{1-e^{-(\lambda_1+\lambda_2)c}\},
$$
while the denominator is the expression in braces. Their ratio is
$$
\frac{\lambda_1}{\lambda_1+\lambda_2}.
$$