Solution
= Solution
The bus may have arrived before observation began or after observation ended. Its compatible event set is $(-\infty,2)\cup(20,\infty)$, so, with endpoint conventions chosen to match whether arrivals exactly at 2 or 20 would be seen, the contribution is
$$
\mathbb P(T<2)+\mathbb P(T>20)=F(2^-)+S(20).
$$
This is <doubly censored data>, because neither the side nor the event time is known.