原式=(164-12/13)/(41+1/39)
=(164-12/13)*39/(41*39+1)
=(4*41*39-12*3)/[(40+1)(40-1)+1]
=[4*(40+1)(40-1)-36]/(1600-1+1)
=[4*(1600-1)-36]/1600
=(4*1600-40)/1600
=4-1/40
=3.975