Four numbers are chosen at random

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

Statement-1 : The probability that the chosen numbers when arranged in some order will form

an $\mathrm{AP}$ is $\frac{1}{85}$

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