1/4+3/7 1/2-3/8 5/6-(1/2-2/7) 7/18+1/27

1/4+3/7=7/28+3*4/28=7/28+12/28=19/28 1/2-3/8=4/8-3/8=1/8 5/6-(1/2-2/7)=5/6-(7/14-4/14)=5/6-3/14=5*7/42-3*3/42=35/42-9/42=26/42=13/21 7/18+1/27=7*3/54+2/54=21/54+2/54=23/54