1) -1/4 + 3/5 = (-5 + 12) / 20 = 7/20;2) 9/11 + (-2/5) = (45 - 22) / 55 = 23/55;3) -20/21 + 3/7 = (-203 + 321) / 147 = (-60 + 63) / 147 = 3/147 = 1/49;4) -8 9/14 + 3 3/7 = -8 + 3 + (3 - 9)/14 = -5 - 6/14 = -5 - 3/7 = -5 3/7;5) 7 5/12 + (-3 7/24) = 7 - 3 + (5 - 7)/12 = 4 - 2/12 = 4 - 1/6 = 3 5/6;6) -6 11/12 + (-8 13/18) = -6 - 8 + (-11 - 13)/12 = -14 - 24/12 = -14 - 2 = -16;7) -5 12/35 + 10 = -5 + 10 - 12/35 = 5 - 12/35 = 175/35 - 12/35 = 163/35;8) -11 7/9 + 8 2/15 = -11 + 8 - (7 + 2)/9 = -3 - 9/9 = -3 - 1 = -4;9) -3 1/12 + 1/6 = -3 + 1 - 1/12 = -2 11/12;10) 3 6/7 + (-6 4/9) = 3 - 6 + (6 - 4)/9 = -3 + 2/9 = - 3 + 2/9 = -3 + 2/9;11) 9 1/6 + (-5 3/4) = 9 - 5 + (1 - 3)/6 = 4 - 2/6 = 4 - 1/3 = 3 2/3;12) -3 8/9 + (-2 1/12) = -3 - 2 + (-8 - 1)/9 = -5 - 9/9 = -5 - 1 = -6.
1) -1/4 + 3/5 = (-5 + 12) / 20 = 7/20;
2) 9/11 + (-2/5) = (45 - 22) / 55 = 23/55;
3) -20/21 + 3/7 = (-203 + 321) / 147 = (-60 + 63) / 147 = 3/147 = 1/49;
4) -8 9/14 + 3 3/7 = -8 + 3 + (3 - 9)/14 = -5 - 6/14 = -5 - 3/7 = -5 3/7;
5) 7 5/12 + (-3 7/24) = 7 - 3 + (5 - 7)/12 = 4 - 2/12 = 4 - 1/6 = 3 5/6;
6) -6 11/12 + (-8 13/18) = -6 - 8 + (-11 - 13)/12 = -14 - 24/12 = -14 - 2 = -16;
7) -5 12/35 + 10 = -5 + 10 - 12/35 = 5 - 12/35 = 175/35 - 12/35 = 163/35;
8) -11 7/9 + 8 2/15 = -11 + 8 - (7 + 2)/9 = -3 - 9/9 = -3 - 1 = -4;
9) -3 1/12 + 1/6 = -3 + 1 - 1/12 = -2 11/12;
10) 3 6/7 + (-6 4/9) = 3 - 6 + (6 - 4)/9 = -3 + 2/9 = - 3 + 2/9 = -3 + 2/9;
11) 9 1/6 + (-5 3/4) = 9 - 5 + (1 - 3)/6 = 4 - 2/6 = 4 - 1/3 = 3 2/3;
12) -3 8/9 + (-2 1/12) = -3 - 2 + (-8 - 1)/9 = -5 - 9/9 = -5 - 1 = -6.