五年级奥数专题简便运算.doc

此文档收集于网络，如有侵权请联系网站删除五年级奥数专题解小例题】例1 用简便方法计算下面各题.(1)(4.87.58.1)(2.42.52.7) 解：(1)解法一：(4.87.58.1)(2.42.52.7)=(487581)(242527)=(12425381)(642539)=(12100381)(610039)=(1281)(69)=(2699)(69)=29=18解法二：(4.87.58.1)(2.42.52.7)=(4.82.4)(7.52.5)(8.12.7)=233=18(2)0.1250.250.564解法一：0.1250.250.564=0.1250.250.5(248)=(0.1258)(0.254)(0.52)=111=1解法二：0.1250.250.564=0.125(0.250.5)(88)=(0.1258)(0.1258)数四则混合运算简算=11=1解法三：0.1250.250.564=(640.5)0.250.125=32(0.50.5)(0.50.50.5)=(320.5)0.50.50.50.5=(160.5)0.50.50.5=(80.5)0.50.5=(40.5)0.5=20.5=1通过第(2)题三种算法，你认为哪一种最简便？你还有没有其它的简便解法？(3)3.754.862.50.48解法一：3.754.862.50.48= 37.50.4862.50.48=(37.562.5)0.48=1000.48=48解法二：3.754.862.50.48=3.754.86.254.8=(3.756.25)4.8=104.8=48(4)1.350.610.350.61=(1.350.35)0.61=10.61=0.61例2 看一看下面的算式有什么特点？运用什么运算定律可以使计算简便？(1)1.561.70.441.70.7(2)11.727.85(2.260.46)解：(1)1.561.70.441.70.7=1.7(1.560.44)0.7=1.720.7=3.40.7=2.7(2)11.727.85(2.260.46)=11.727.852.72=11.722.727.85=97.85=1.15例3 计算：0.10.30.50.70.970.99分析：从0.1到0.9，前后两个数相差0.2，从0.11到0.99前后两个数相差0.02.解：0.10.30.50.70.970.99=(0.10.30.50.70.9)(0.110.130.19)(0.210.230.29)(0.910.930.99)=2.5(0.150.25)(0.2550.25)(0.950.25)=2.5(0.10.20.9)50.259=2.522.52.25=27.25【练习】1、用简便方法计算下面各题.(1)5.517.36.75.5 (2)13.70.258(3)32.85.67.2 (4)4.62.540(5)12.5338 (6)500.470.2(7)1017. (8)10.154(9)42.62.777.23 (10)16.416.40.5(11)2.184.657.824.35 (12)12.482.723.28(13)(2502.5)4 (14)470.535(15)(1251.25)8 (16)77510.99.1225cinquain n. 五行诗slogan n. 标语；口号(17)12.42.687. (18)71.78531.785Mexico n. 墨西哥（拉丁美洲国家）southeastern adj. 东南方的；(19)5.25153.7515 (20)18.41.718.48.3live on 继续存在；继续生存(be) scared to death 吓死了(21)7.65.37.63.77.6 (22)45.6387.638dial vt. 拨（电话）(23)(0.450.061.5)0.15 (24)2.75542. 6554(25)1.258.8 (26)0.8910.1(27)255.2640 (28)0.1253225quake n. 地震compete vi. 比赛；竞争(29)0.360.50.3