1/4+2/5 2/3+1/4 5/7-1/6 3/4-1/3

1/4+2/5=5/20+8/20=13/20 2/3+1/4=8/12+3/12=11/12 5/7-1/6=30/42-7/42=23/42 3/4-1/3=9/12-4/12=5/12