1、 街心广场街心广场（建议一课时完成）（建议一课时完成）第三单元第三单元 小数乘法小数乘法 四年级下册 课后课后作业作业探索探索新知新知1课堂探究点课堂探究点2课时流程课时流程课堂课堂小结小结当堂当堂检测检测20米米30米米探究点探究点 积的小数位数与乘数的小数位数的关系积的小数位数与乘数的小数位数的关系先说一说街心广场上的数学信息，再算一算，填一填。先说一说街心广场上的数学信息，再算一算，填一填。街心广场街心广场花坛花坛地砖地砖面积面积/平方米平方米淘气在计算地砖的面积时遇到了困难，你能帮帮他吗？淘气在计算地砖的面积时遇到了困难，你能帮帮他吗？0.30.2 （）0.3米米3分米分米0.2米米2
2、分米分米326（平方分米）（平方分米）6平方分米平方分米0.06（平方米）（平方米）0.30.20.06（平方米）（平方米）0.3米米0.2米米321米米1米米0.01平方米平方米6个个0.01是是0.06平方米。平方米。0.06 平方米平方米结合上面的计算过程，想一想乘数和积之间有什么关系。结合上面的计算过程，想一想乘数和积之间有什么关系。3 0 2 06 0 03 260.3 0.20.0 6积的小数位数与乘数的小数位数有什么关系？算一算，积的小数位数与乘数的小数位数有什么关系？算一算，想一想。想一想。0.1240.31.20.40.30.1320.130.2第一个乘数第一个乘数的小数位数
3、的小数位数第二个乘数第二个乘数的小数位数的小数位数积的小数位积的小数位数数0.260.026011112202213小试牛刀小试牛刀（源于（源于典中点典中点）1算一算。算一算。(1)10101000.1 8(2)11011001102填一填。填一填。(1)一个乘数扩大到原来的一个乘数扩大到原来的10倍，另一个乘数扩大到原倍，另一个乘数扩大到原来的来的100倍，积就扩大到原来的倍，积就扩大到原来的()倍。倍。(2)一个乘数缩小到原来的一个乘数缩小到原来的 ，另一个乘数也缩小到，另一个乘数也缩小到原来的原来的 ，积就缩小到原来的，积就缩小到原来的()。1101101000110003把表格补充完整
4、，你发现了什么？把表格补充完整，你发现了什么？我发现：我发现：_。算式算式第一个第一个乘数乘数的小数位数的小数位数第二个乘数第二个乘数的小数位数的小数位数积的小积的小数位数数位数0.0330.09 51.57.5 1.40.20.28 202001112两个乘数一共有几位小数，积就有几位小数两个乘数一共有几位小数，积就有几位小数(答案不唯一答案不唯一)4根据第一栏的积快速写出后面每栏的积。根据第一栏的积快速写出后面每栏的积。乘数乘数12121.21.2121201.2乘数乘数15150151.51.50.150.15积积180 1800181.818180.18归纳总结：归纳总结：（讲解源于（
5、讲解源于典中点典中点）两个数相乘，每一个乘数都乘两个数相乘，每一个乘数都乘(或除以或除以)一一个不为个不为0的数，它们的积就乘的数，它们的积就乘(或除以或除以)这这两个不为两个不为0的数的乘积。的数的乘积。小试牛刀小试牛刀（教材（教材P39练一练）练一练）1.你会计算这块拼图的面积吗？想一想，算一算。你会计算这块拼图的面积吗？想一想，算一算。（1）与同伴交流你的想法。）与同伴交流你的想法。（2）结合计算过程说一说，积的）结合计算过程说一说，积的 小数位数与乘数的小数位数小数位数与乘数的小数位数 有什么关系？有什么关系？略。略。0.30.30.09(平方米平方米)积的小数位数是乘数的小数位数之和
6、。积的小数位数是乘数的小数位数之和。2.根据第一栏的积很快写出后面每栏的积。根据第一栏的积很快写出后面每栏的积。乘数乘数363.6363.60.36乘数乘数242.42.4242.4积积8648.6486.486.40.8643.淘气的计算器上的小数点无法显示了，你能帮他得到淘气的计算器上的小数点无法显示了，你能帮他得到正确答案吗？正确答案吗？4.明明每天上学和放学都要乘坐一次公交车，每乘一次公交明明每天上学和放学都要乘坐一次公交车，每乘一次公交车花车花0.2元。明明的公交卡里还剩元。明明的公交卡里还剩3元，够他一周元，够他一周5天上学天上学和放学用吗？和放学用吗？0.220.4（元）（元）0
7、.452（元）（元）够他一周够他一周5天上学和放学用。天上学和放学用。5.根据根据1312156，在，在 里填上适当的数。里填上适当的数。13 1.2 1.3 1.21.312 13 0.121.30.12 1.31200.13 1.2 130 1.2点拨：答案不唯一。点拨：答案不唯一。易错辨析易错辨析5判断。判断。(对的画对的画“”，错的画，错的画“”)(1)2.45的积的小数位数有的积的小数位数有0位。位。()(2)0.1258的积有三位小数。的积有三位小数。()辨析：两个乘数一个共有几位小数，积就有辨析：两个乘数一个共有几位小数，积就有几位小数。几位小数。版权申明本文部分内容，包括文字、
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