2.4-2.4*4/7-3/7 =2.4*(1-4/7)-3/7 =2.4*3/7-3/7 =(2.4-1)*3/7 =1.4*3/7 =0.6 3*【（2/15+1/12）*1/15】 =3*[（2/15+1/12)*1/5] =3*[(8/60+5/60)*1/5] =3*13/60*1/5 =13/1001/5÷〔（2/3+1/5）*1/15〕=1/5÷〔13/15*...