In the x- y plane, there are 4 points (0,0), (0,4), (5,4), and (5,0). If these 4 points makes a rectangle, what is the probability that x+y<4?
Pick one
A) 2 / 3  B) 2 / 5  C) 3 / 4  D) 3 / 7  E) 5 / 8

Rationale: the line y = - x + 4 intersects the rectangle and these three points of intersection ( 0,0 ) , ( 0,4 ) and ( 4,0 ) form a triangle . the points below the line y = - x + 4 satisfy x + y < 4 . the area of this triangle is ( 1 / 2 ) ( 4 ) ( 4 ) = 8 the area of the rectangle is 20 . p ( x + y < 4 ) = 8 / 20 = 2 / 5 the answer is b .
Answer: B