9. Two people go to the same swimming pool between 2:00p.m. and 5:00p.m. at random time and each swims for one hour. What is the chance that they meet?
(A) $\frac{1}{9}$;
(B) $\frac{2}{9}$;
(C) $\frac{1}{3}$;
(D) $\frac{4}{9}$;
(E) $\frac{5}{9}$.
9. Answer: (E).
Let $x$ and $y$ denote the numbers of hours after 2:00p.m. that the first and the second person visits the swimming pool, respectively. Then
$$
0 \leq x \leq y \leq 3 \text { and } y \leq x+1 .
$$

So the chance that they meet is $\frac{5 / 2}{9 / 2}=\frac{5}{9}$.