Use the midpoint formula for this question (x1+x2/2, y1+y2/2). In this case, x1 would be 3 and x2 would be 5. 3+5=8, and 8/2 is 4. Similarly, y1 would be 6 and y2 would be -2. 6+(-2)=4, and 4/2= 2. So, the midpoint would be (4,2)
The probability of choosing one of them is 2 / 80 .
the probability of choosing
the other one is 1 / 79 .
The probability of both things happening is
(2/80) x (1/79) = 1/3160