Twenty five of King Arthur's knights are seated at their customary round table. Three of them chosen-all choices of three being equally likely-and are sent off to slay a troublesome dragon. Let P be the probability that at least two of the three had been sitting next to each other . If P is written as a fraction in lowest terms, What is the sum of numerator and denominator?

译文:亚瑟王的25位骑士坐在他们的圆桌旁,选出3名骑士(等概率的)去斩妖龙。设P是选出的3位中至少有两位座次相邻的概率。如果P写作既约分数,求分子与分母之和。

(第一届AIME1983 第七题)