1/4-1/5=5/20-4/20=1/20
1/18+1/6=1/18+3/18=2/9
1/2-1/8=4/8-1/8=3/8
7/11+5=7/11+55/11=62/11
1/3+1/4=4/12+3/12=7/12
2-1/3=6/3-1/3=5/3