Катюша1200 1) -5/24+11/36= -15/72+22/72=7/72   
2)-1/5+ (-3/5)=-4/5
3)5/7 + (-6/7)= -1/7
4)- 7/9 + 8/9 =1/9
5)- 2/5+ (-7/15 )= -13/15
6)-1/3 +1/2 =-2/6+3/6=1/6
7)-5/18+ 1/24=-20/72+3/72=-17/72