1题=1.7/4+8.3/4=1/4(1.7+8.3)=2.5
2 =8/9*3/4+8/9(7/16-4/16)=2/3+1/6=5/6
3 =(50*25*8)/(2*5)=5*25*2*4=10*100=1000
4 =1+6/7=13/7