解:(5/7-1/14+5/6)÷5/42=(5/7-1/14+5/6)x42/5=5/7x42/5-1/14x42/5+5/6x42/5=6-3/5+7=13-3/5=12又2/5
=(10/14-1/14+5/6)×42/5=(27/42+35/42)×42/5=62/42×42/5=62/5=12.4