3.1. At a sumo wrestling tournament, 20 sumo-tori (sumo wrestlers) arrived. After weighing, it was found that the average weight of the sumo-tori is 125 kg. What is the maximum possible number of wrestlers who weigh more than 131 kg, given that according to sumo rules, people weighing less than 90 kg cannot participate in the competition?
Answer: 17.

Solution: Let $n$ be the number of sumo-tori that weigh more than 131 kg. Their total weight is more than $131 n$ kg, and the total weight of the remaining ones is no less than $90(20-n)$. Therefore, $\frac{131 n+90(20-n)}{20}<125$, from which $41 n<35 \cdot 20$, i.e., $n<\frac{700}{41}=17 \frac{3}{41}$. The largest integer $n$ satisfying this condition is 17. If 17 sumo-tori weigh $131 \frac{3}{17}$ kg each, and the remaining 3 weigh 90 kg each, the conditions of the problem are met.