Solution
= Solution
Time to the first of $A$ and $B$ is exponential with rate $\theta+\phi$ and mean $1/(\theta+\phi)$. The expected total <person-time at risk> is
$$
\mathbb E[x_+]=\frac n{\theta+\phi}.
$$
= Solution
Time to the first of $A$ and $B$ is exponential with rate $\theta+\phi$ and mean $1/(\theta+\phi)$. The expected total <person-time at risk> is
$$
\mathbb E[x_+]=\frac n{\theta+\phi}.
$$