4・214 Three people, A, B, and C, are playing a game: On three cards, integers $p$, $q$, and $r$ ($0<p<q<r$) are written. The three cards are mixed and distributed to A, B, and C, with each person getting one card. Then, according to the number on each person's card, the corresponding number of marbles is given to each person. After that, the cards are collected, but the marbles are kept by the individuals. This process is repeated for more than two rounds (each round includes mixing the cards, distributing the cards, giving out the marbles, and collecting the cards). After the final round, A, B, and C have a total of 20, 10, and 9 marbles, respectively. It is known that B received $r$ marbles in the last round. Who received $q$ marbles in the first round?
[Solution] Let the game have proceeded for $n$ rounds, then
$$
n(p+q+r)=20+10+9=39 \text {, }
$$

Since $00$ is contradictory. Therefore, the number of marbles $C$ obtained in the last round must be $p$, and the number of marbles $A$ obtained in the last round is $q$, thus we have
$$
2 r+q=20,2 p+r=10,2 q+p=9 .
$$

Solving these equations, we get
$$
p=1, q=4, r=8 \text {. }
$$