13.18. Assume the and miss distances of darts thrown at a bulls-eye dart board are Gaussian with zero mean and variance .

(a) Determine the probability that a dart will fall between and .

(b) Determine the radius of a circle about the bulls-eye that contains 80% of the darts thrown. (c)

Consider a square with side in the first quadrant of the board. Determine so that the probability that a dart will fall within the square is 0.07.