五年级奥数题：小数的巧算(A).doc

小数的巧算（1）教学内容：小数的巧算教学目标：培养学生快速做出小数计算题的方法与技巧。教学重难点:小数巧算的计算方法。教学方法：凑整法；交置法；去括号发。例1.计算 1.135+3.346+5.557+7.768+9.979=_.例2. 计算 1.996+19.97+199.8=_.例3. 计算 9.8+99.8+999.8+9999.8+99999.8=_.例4. 计算 6.11+9.22+8.33+7.44+5.55+4.56+3.67+2.78+1.89=_.例5. 计算 1.1+3.3+5.5+7.7+9.9+11.11+13.13+15.15+17.17+19.19=_.例6. 计算 2.894.68+4.686.11+4.68=_.例7. 计算 17.4837-17.4819+17.4882=_.例8. 计算 1.250.322.5=_.例9. 计算 754.7+15.925=_.例10. 计算 28.6767+3228.67+573.40.05=_.例11 1.135+3.346+5.557+7.768+9.979=_.例12. 1.996+19.97+199.8=_.例13. 6.11+9.22+8.33+7.44+5.55+4.56+3.67+2.78+1.89=_.例14. 1.1+3.3+5.5+7.7+9.9+11.11+13.13+15.15+17.17+19.19=_例15. 2.894.68+4.68 6.11+4.68=_.例16. 17.4837-17.4819+17.4882=_.例17. 1.25 0.322.5=_.例18. 754.7+15.925=_.例19. 28.6767+32286.7+573.4 0.05=_.例20. 172.46.2+27240.381028个0963个0例21. 0.0001810.00011例22.34+23.45+34.56+45.67+56.78+67.89+78.91+89.12+91.231994个01996个0例23.a= 0.000105 b=0.00019 计算a+b a-b ab ab例24. 4.75-9.64+8.25-1.36例25. 3.71-2.74+4.7+5.29-0.26+6.3例26. (5.25+0.125+5.75) 8例27. 34.58.23-34.5+2.7734.5例28. 6.250.16+2640.0625+5.26.25+0.62520例28. 0.035935+0.035+30.035+0.07610.5例29. 19.9837-199.81.9+19980.82例30. 13.59.9+6.5+5.7510.1例31. 0.1250.250.564例32.11.843-8600.09例33.32.14+64.280.53780.25+0.537864.280.75-864.280.1250.5378例34. 0.88812573+9993例35. 1998+199.8+19.98+1.998二、解答题1. 计算 172.46.2+27240.382. 计算 0.0001810.00011 964个0 1029个0 3. 计算 12.34+23.45+34.56+45.67+56.78+67.89+78.91+89.12+91.234. 下面有两个小数: a=0.000105 b=0.00019 1994个0 1996个0求a+b, a-b, ab, ab.1996个02000个05.a= 0.000125 b=0.0008 求a+b, a-b, ab, ab.1. 27.7852. 221.766原式=(2-0.004)+(20-0.03)+(200-0.2)=222-(0.004+0.03+0.2)=221.7663. 111109提示:仿上题.4. 49.555. 103.25原式=1.1(1+3+9)+1.01(11+13+19)=1.125+1.0175=103.256. 46.87. 1748原式=17.4837-17.4819+17.4882=17.48(37-19+82)=17.48100=17488. 1原式=(1.250.8)(0.42.5)=11=19. 750原式=754.7+5.3(325)=75(4.7+5.3)=7510=75010. 2867原式=28.6767+3228.67+28.67(200.05)=28.67(67+32+1)=28.67100=286711. 原式=172.46.2+(1724+1000)0.38=172.46.2+17240.38+10000.38 =172.46.2+172.43.8+380=172.4(6.2+3.8)+380 =172.410+380=1724+380=210412. 181是三位,11是两位,相乘后18111=1991是四位,三位加两位是五位,因此1991前面还要添一个0,又963+1028=1991,所以0. 0001810.00011=0.0001991 964个0 1029个0 1993个013. 9个加数中,十位、个位、十分位、百分位的数都是19，所以原式=11.11(1+2+9)=11.1145=499.9514. a是小数点后有(19