1. -3,9+8,6+4,7+3,9-4,7 = (3,9-3,9)+(4,7-4,7)+8,6 = 0+0+8,6 = 8,6
2. 4 3/8-3 3/7-9,5+5 1/8 = ((4 3/8+5 1/8)-9,5)-3 3/7 = (9 4/8-9,5)-3 3/7 = (9,5-9,5)-3 3/7 = 0-3 3/7 = -3 3/7
3. 4 9/14-5/12-3 3/14-3 1/12+1 1/14 = (4 9/14-3 3/14+1 1/14)-(5/12+3 1/12) = 2 7/14-3 6/12 = 2,5-3,5 = -1
4. 3 1/3-0,8-2 3/4+2,5+0,3+1 7/12 = ((3 1/3-2 3/4)+1 7/12)+((2,5+0,3)-0,8) = ((3 4/12-2 9/12))+(2,8-0,8) = (7/12+1 7/12)+2 = 2 2/12+2 = 2 1/6+2 = 4 1/6