1) (3/4 + 1/5) * 5/19 = ( 15/20 + 4/20) * 5/19 = 9/20 * 5/19 = 45/380
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 = 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 = 0,1