求助一道feifei宝典数学题

7、一直线L过点A(5,0)，B(0,2)，坐标原点为O，点P(x,y)为三角形OAB中的一点，问：y<x的概率为多少？
Answer: 5/7

Y=-2/5 X+2; Y=X>>>X=10/7; [5*10/7]/[5*2]=5/7

这个是答案，还是看不懂。

In coordinate-plane,the area below line y=x means  y<x.

you can see that the line y=x  splits the triangle OAB into two small triangles, and the probability asked is the ratio of the area of the triangle below line y=x to the area of triangle OAB.

the line which goes through (5,0),(0,2) is Y=-2/5 X+2, and it intersects line y=x at (10/7,10/7),then you can work the ratio out.