原式=7.2/衫尘轿判（或帆禅1/4）+2.8*4 =7.2*4+2.8*4 =(7.2+2.8)*4 =10*4 =40
7.2÷0.25+2.8x4=7.2*4+2.8x4=4*（7.2+2.8）=4*10=40
