解:7/8-2/3=(7x3)/(8x3)-(2x8)/(3x8)=21/24-16/24=5/24
7/8=21/242/3=16/247/8-2/3=21/24-16/24=(21-16)/24=5/24
答案是5/24
8/7一2/3二答案是5/24