13. A student participates in military training and must shoot 10 times. In the 6th, 7th, 8th, and 9th shots, he scored 9.0, 8.4, 8.1, and 9.3 points, respectively. The average score of his first 9 shots is higher than the average score of his first 5 shots. If he wants the average score of 10 shots to exceed 8.8 points, how many points does he need to score at least in the 10th shot? (The points scored in each shot are accurate to 0.1 points)
Three, 13. From the given information, the average score of the first 5 shots is less than $\frac{9.0+8.4+8.1+9.3}{4}=8.7$, the total score of the first 9 shots is at most $8.7 \times 9-0.1=78.2$. Therefore, the 10th shot must score at least $8.8 \times 10+0.1-78.2=9.9$ (rings).