a.（40+8）×25=40×25+8×25=1000+200=1200

b. 36×34+36×66=36×（34+66）=3600 c .78×102=78×（100+2）=7800+156=7956

d. 31×99=31×(100-1)=3100-31=3069 e. 25×39=25×(40-1)=1000-25=975

f. 83+83×99=83×(1+99)=8300 g. 91×31-91=91×(31-1)=2730 h. 0.3×63+99.7×63

=63×(0.3+99.7)=6300 i. 8.8×27+91.2×27=27×(8.8+91.2)=2700 j.125×81=125×(80+1)=125×80+125×1=10000+125=10125

追答：A.(1/69+2/71)×23+25÷71 =1/69×23+2/71×23+25/71 =1/3+(46/71+25/71) =1/3+1 =4/3 B.(1+1/2)×(1-1/2)×(1+1/3)×(1-1/3)×........×(1+1/9)×(1-1/9) =3/2×1/2×4/3×2/3...×10/9×8/9 =1/2×10/9(中間的都約去了） =5/9 C.1/27+505/2727+131313/272727 =1/27+5*101/(27*101)+13*10101/(27*10101) =1/27+5/27+13/27 =19/27 E. 35×37+65×37 =37×(35+65) =3700 F. 25×404 =25×(400＋4) =25×400＋25×4 =10000＋100=10100