Alexakrestik 1/8+2/8= 3/8
6/9-5/9=1/9
6/12-5/12= 1/12
5/12-2/9= 15/36-8/36= 7/36
1/8+7/12= 3/24+14/24= 17/24
3/4-1/6= 9/12-2/12= 7/12
5/9+3/4= 20/36+27/36= 47/36
23/40-3/8= 23/40-15/40= 8/40= 1/5 либо 0,2

asdcvfgbhnjm Будем приводить к общему знаменателю
1) 1/8 + 2/8 = 3/8
2) 6/9 - 5/9 = 1/9
3) 6/12 - 5/12 = 1/12
4) 20/36 - 8/36 = 12/36 = 1/3
5) 3/24 + 14/24 = 17/24
6) 9/12 - 2/12 = 7/12
7) 20/36 + 27/36 = 47/36 = 1 целая 11/36
8) 23/40 -15/40 = 8/40 = 1/5 
9) 36/140 - 15/140 = 11/140