Four numbers are chosen at random (without replacement) from the set $\left\{ {1,2,3,....20} \right\}.$

Statement - 1: The probability that the chosen numbers when arranged in some order will form an AP is ${1 \over {85}}.$

Statement - 2: If the four chosen numbers form an AP, then the set of all possible values of common difference is $\left( { \pm 1, \pm 2, \pm 3, \pm 4, \pm 5} \right).$