6/7-5/6=(1-1/7)-(1-1/6)=1/6-1/7=(7-6)/7x6 =(6-5)/7x6=1/42 9/4+9/5=9x9/4x5=81/209/4+9/5=(9x5+9x4)/4x5=9(5+4)/4x5=9x9/4x5=81/20
