急，再现等两道简算题答案！
1/2+1/6+1/12+1/20 ===================================== 297/385+2997/3885+29997/38885 谢
1/2+1/6+1/12+1/20 =1-1/2+1/2-1/3+1/3-1/4+1/4-1/5 =1-1/5 =4/5 297/385+2997/3885+29997/38885 =(27*11)/(35*11)+(27*111)/(35*111)+(27*1111)/(35*1111) =27/35+27/35+27/35 =（27*3)/35 =81/35
答：用交换律、结合律、凑整十整百详情>>
答：设1994=a详情>>
答：1.450÷2×5 ＝450×2.5 ＝450×2＋450÷2 ＝900＋225 ＝1125 2.切成"井"字 3.什么东东啊? 4.解:设钢笔是x元。 10－...详情>>
