1) 3/8 + 6/20 = 3/8 + 3/10 = 3(10 + 8)/80 = 3 x 18/80 = 3 x 9/40= 27/40
2) -2,18 + 3,6 = 1,42
3) (-15/22):(10/33) = (-15/22) x (33/10) = - (15 x 33) / (22 x 10) = - (3 x 3)/(2 x 2) = -9/4
4)-25/27 x 18/15 = - (25 x 18) / (27 x 15) = - ( 5 x 2) / (3 x 3) = - 10/9
5) 2,(18)= (218 - 2)/99 = 216/99 = 24/11