svetazuna  (2 3/5 - 5/8) : 19 3/4 = 1/10,

1) 2 3/5 - 5/8 = 13/5 - 5/8 = 104/40 - 25/40 = 79/40 = 1 39/40,
2) 1 39/40 : 19 3/4 = 79/40 : 79/4 = 79/40 * 4/79 = 4/40 = 1/10