推荐回答(3个)
典型例题】
[例1] 学校有20个足球,篮球比足球多 ,篮球有多少个?
[例2] 学校有20个足球,足球比篮球多 ,篮球有多少个?
[例3] 学校有20个足球,篮球比足球少 ,篮球有多少个?
[例4] 学校有20个足球,足球比篮球少 ,篮球有多少个?
对比:从以上四道题的结构上看相同点都是已知足球的个数,求篮球的个数。不同点是单位“1”不同,多少不同。
从思路上看,都是根据带有分率的句子确定单位“1”,根据单位“1”的已知和未知确定解法。
从四道题的解题方法上看,单位“1”已知用乘法,单位“1”未知用方程或用除法解答,根据两个数量的多少确定加或减。
①、③两题的共同点单位“1”已知用乘法,不同点,比单位“1”多,1+,比单位“1”少1-。
②、④两题的共同点单位“1”未知,用方程或用除法,不同点是等量关系不同,如果用除法解答相同点都是用已知量÷已知量对应的分率。
[例5] 一支工程队修一条公路,每一天修了38米,第二天修了52米,两天正好修全长的 。这条路全长多少米?
分析:全长是单位“1”,单位“1”未知,等量关系是全长的 正好等于两天修的和。
解:设全长为 米。
或 (米)
[例6] 一本书200页,第一天看全书的 ,第二天看全书的 ,两天共看多少页?
分析:全书的总页数是单位“1”,单位“1”是已知的,求两天共看多少页,也就是求200页的 与 的和是多少?
列式是 (页)
通过⑤⑥两题的分析与解答,会使同学们更加清楚的看到较复杂的分数乘、除法应用题关键要找出量与率对应的关系。当单位“1”已知时,所求量和分率对应,单位“1”未知时,已知量和分率对应。
【模拟试题】(答题时间:40分钟)
1. 红光小学有男生120人,女生比男生多 ,有女生多少人?
2. 学校十月份用水48吨,十一月比十二月节省 。十一月份用水多少吨?
3. 林场去年造林1260公顷,超过原计划的 ,原计划造林多少公顷?
4. 学校买了一批新书,其中故事书有30本,科技书有18本,共占这批新书的 。这批新书有多少本?
5. 修路队修一条公路,第一天修全长的 ,第二天修全长的 ,第二天比第一天多修24千米。这条公路全长多少千米?
6. 一块长方形地,长120米,宽比长短 。这块地的面积是多少平方米?
7. 一套课桌椅的价钱是60元,其中椅子的钱数是课桌的 ,椅子的价钱是多少元?
8. 食品厂生产儿童饼干6吨,比生产的果汁饼干多 。两种饼干一共生产多少吨?
9. 足球队有高年级学生21人,比低年级多3人,低年级中有 是女生,足球队有女生多少人?
10. 水果店有苹果38筐,梨42筐,这两种水果占总数的 ,水果店有水果共多少筐?
11. 某学校共有1200人,其中女生占总人数的 。后来又转进一些女生,这时女生人数占全校人数的 ,这个学校现在有多少人?
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