[1又1/4-(3/8+1/6-3/4)乘以24]除以5=[5/4-3/8*24-1/6*24+3/4*24]/5=(5/4-9-4+18)*1/5=(5/4+5)*1/5=5/4*1/5+5*1/5=1/4+1=5/4
