25*2.4/25-2.1 =2.4*25/25 - 2.1=2.4-2.1=0.3.2又2/3-1.8+1又5/6 =3 - 1/3 - 2+ 0.2 + 2 - 1/6=3 - (1/3+ 1/6) + 1/5=3 - 1/2 +1/5=3 - 5/10 + 2/10=3 - 3/10=2又7/10.15.73-6.17+4.27-3.83=15.73+ 4.27 -（6.17+3.8...