1/7-5/7= -4/7
1/2+5/6=3/6+5/6=8/6=4/3
2/5-3/4=8/20-15/20=-7/20
3/4*7/11=21/44
-2/15*25/6=-50/90=-5/9
4/7:5/3=4/7*3/5=12/35
7/5-7/3*15/14=7/5-105/42=7/5-5/2=14/10-25/10= -11/10
8/5-3/4:9/8=8/5-3/4*8/9=8/5-24/36=8/5-2/3=24/15-10/15=14/15
(8/3-2/5)/(7/5)=(40/15-6/15)*5/7=34/15*5/7=170/105=34/21
