6上分数乘分数.ppt
分数和分数相乘,,口算,说说分数和整数相乘的计算方法,说出算式,并口算出结果,下面图中的涂色部分都表示一张的纸 ,,,,,,,,,画斜线的部分各占 的几分之几?,,,,,,,,的 、 的 各是这张纸的几分之几?你能列算式并看图填写出结果吗?,,,,,,=,=,在图中画斜线表示计算结果,再填空。,,,( ),( ),( ),( ),( ),5,3,5,( ),( ),2,( ),( ),4,( ),( ),,,观察例4、例5,你发现积的分子、分母与两个因数的分子、分母各有什么关系?在小组里交流。,,2,,3,×,1,,=,2,,15,,2,,×,4,,=,8,,15,( ),( ),,1,,×,1,,=,1,,8,,,2,( ),( ),4,( ),1,,×,3,,=,3,,8,,,( ),( ),( ),( ),( ),( ),( ),( ),( ),( ),你能先约分再计算吗?试着算一算。,1,1,2,6,9,4,3,8,3,2,3,1,,4,×,2,,=,,4×3,,×,=,,4,8,,9,×,3,,=,,,×,=,,×,,,1,2,,,1,3,,,1,2,分数和分数相乘的计算方法适用于分数和整数相乘吗?为什么?,请用分数和分数相乘的方法计算 下面各题。,2,4,1,1,11,3,5,6,6,11,10,3,,,3,2,分数乘法也可以像下面这样计算。,1,,4,,2,×,2,,3,,1,=,1,,6,4,,2,×,5,,6,,3,=,10,,3,5,,,,,4,,×,4,1,,8,3,,×,5,2,,10,9,,×,6,5,,5,×,15,2,,,,1,1,=,5,1,,,,2,3,,,2,1,=,4,3,,,,4,1,=,20,3,,,,3,1,=,3,2,,⒈ 一台拖拉机每小时耕地 公顷, 小时耕地多少公顷? 小时呢? 先在图中表示出来,再列式计算。,练习九,2,1,,3,1,,3,2,,,公顷,,公顷,,,,,,,,,2,1,,×,3,1,,=,6,1,,(公顷),2,1,,×,3,2,,=,3,1,,(公顷),,,1,1,练习九,⒊ 下面的计算对吗?把不对的改 正过来。,5,×,5,,6,,=,1,,6,×,7,,24,,=,9,,1,8,,21,,,,(1),(2),9,21,5,×,5,,6,=,25,,6,×,7,,24,,=,8,,,,,1,,1,1,1,3,3,1,1,3,3,,,,,?,,,,,,,,,?,,,,,,,看图列算式:,,,,?,,,看图列算式:,,,,,,,?,,,,,,,看图列算式:,,,,看算式画图:,,,,,,练习九,⒋ 算一算,比一比。,,,7,2,,×,2,5,×,5,4,,2,1,,×,2,1,,4,3,,×,4,3,,7,2,,×,7,4,×,5,4,,2,1,,+,2,1,,4,3,,+,4,3,,练习九,⒋ 算一算,比一比。,,,7,2,,×,2,5,×,5,4,,7,2,,×,7,4,×,5,4,,=,=,=,=,7,4,,4,2,5,16,,练习九,⒋ 算一算,比一比。,,,2,1,,×,2,1,,4,3,,×,4,3,,2,1,,+,2,1,,4,3,,+,4,3,,=,=,=,=,4,1,,1,16,9,,2,3,,