Target Precision and confidence

Hello, this one is a bit tricky one but I will explain it the best I can.

I have a series of X, Y coordinates (locations that arrows from a bow and arrow hit a target) that I want to do two things with. First, I want to create a formula that will calculate the smallest diameter circle that will encapsulate all of those coordinates (regardless of their location on the axis) thus calculating precision.

Second, I want to be able to calculate what percentage of additional shots would be able to fall into a certain size box on the same target.

For this example, the coordinates below are applicable (x,y) and both the x and y axis are arbitrary because we are calculating the bow's precision and not accuracy.

4.500,-1.750 2.625,-1.500 2.875,1.875 1.750,1.875 1.375,3.250 0.625,2.500 -0.500,4.375 -1.000,0.375 -1.500,-2.625 -2.250,-3.750

Thoughts or help?

Thanks!