1)0,25+(-4/5)+(-9/20) = 0,25 - 4/5 - 9/20 = 25/100 - 4/5 - 9/20 = 25/100 - 80/100 - 45/100 = -1
2)-0,2+1/6+(-8 1/15) = -0,2 + 1/6 - 8 1/15 = - 6/30 + 5/30 - 8 2/30 = -8 1/10
3)-5,9+(-3 1/4+1 3/20) = -5,9 - 2 1/10 = - 5 9/10 - 2 1/10 = -8
4)6,7+(2 1/3-9 2/5) = 6,7 - 7 1/15 = - 11/30