Solution
We have R = {(1, 39), (2, 37), (3, 35), (4, 33), (5, 31), (6, 29), (7, 27), (8, 25), (9, 23), (10, 21), (11, 19), (12, 17), (13, 15), (14, 13), (15, 11), (16, 9), (17, 7), (18, 5), (19, 3), (20, 1)}.
Since (1, 39) ∈ R but (39, 1) ∉ R, therefore R is not symmetric. Clearly R is not reflexive. Now, (15, 11) ∈ R and (11, 19) ∈ R but (15, 19) ∉ R. So R is not transitive.