1、第3招 巧算小数加减法 QD 四年级下册 学习第3单元后使用用简便方法计算：7.136.966.917.22 70.13算式中的四个数都与整数7比较接近，所以将7作为基准数经典例题 70.0470.0970.227.136.966.917.22(70.13)(70.04)(70.09)(70.22)74(0.130.040.090.22)280.2228.22规范解答：13提示：点击进入题组训练运用加法运算律简算运用减法的性质简算运用凑整法简算运用基准数法简算2456789101112用配对求和法简算104.614.615.264.64.74运用加法运算律简算技 巧 1 5.264.744.6
2、加法交换律2.2.66.923.40.08(2.63.4)(6.920.08)6713加法分配律311.34(7.342.25)11.347.342.25运用减法的性质简算技 巧 2 42.251.754.2.37(2.41.63)2.371.632.442.41.62.372.41.63运用凑整法简算技 巧 3 533.2819.4116.6220.5933.2816.62(19.4120.59)33.2816.6219.4120.5949.9409.96.3.561.722.44 3.562.441.72 61.724.28运用基准数法简算技 巧 4 7.0.90.990.9990.999
3、91111(0.10.010.0010.0001)(10.1)(10.01)(10.001)(10.0001)40.11113.8889以1为基准8.9.69.79.89.910101010(0.40.30.20.1)(100.4)(100.3)(100.2)(100.1)40139以10为基准9.10.0210.19.889.751040.020.10.120.25(100.02)(100.1)(100.12)(100.25)400.2539.75以10为基准10.15.414.615.314.815.71550.40.40.20.30.7(100.4)(150.4)(150.3)(150.2)(150.7)750.875.8以15为基准用配对求和法简算技 巧 4 11.1.21.41.61.83.63.8项数(3.81.2)0.2114 等差数列求和公式：(首项末项)项数2原式(1.23.8)142 35项数=(末项首项)公差+112.0.10.30.59.79.9项数(9.90.1)0.2150 等差数列求和公式：(首项末项)项数2原式(0.19.9)502250项数=(末项首项)公差+1
