1) (3/4 + 1/5) * 5/19 = (15/20 + 4/20) * 5/19 = 19/20 * 5/19 = 5/20 = 1/4 = 0,25; 2) (12 1/3 - 7 3/4) * 6/11 = (12 4/12 - 7 9/12) * 6/11 = (11 16/12 - 7 9/12) * 6/11 = 4 7/12 * 6/11 = 55/12 * 6/11 = 5/2 = 2,5; 3) (2 3/5 - 5/8) : 19 3/4 = (2 24/40 - 25/40) : 19 3/4 = (1 64/40 - 25/40) : 19 3/4 = 1 39/40 : 19 3/4 = 79/40 : 79/4 = 79/40 * 4/79 = 1/10 = 0,1.