分数加减法简便计算.ppt

单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,三角形的内角和,灵宝市第一小学 张变霞,加法运算定律有哪些？,加法交换律：,加法结合律：,a+b=b+a,a+b+c=a+(b+c),减法运算定律有哪些？,连减的性质：,a-b-c=a-(b+c),a-(b+c)=a-b-c,这些运算定律在分数加减中能用吗？,5,7,+,2,5,2,5,+,5,7,比较大小：,=,2,3,+,1,4,（,）,+,3,4,2,3,+,（,1,4,3,4,+,）,=,4,5,3,10,2,3,+,2,3,+,1,2,1,4,（,）,4,5,8,-,5,8,-,3,8,=,4,5,8,-,1,3,8,5,8,5,12,+,+,=,5,8,+,3,8,+,5,12,=,1,5,12,=,+,5,12,1,=,3,5,8,=,4,5,8,-,5,8,+,3,8,（,）,用心练一练,4,13,9,19,4,13,+,1,4,1,4,1,8,9,19,8,4,2,5,8,=,4,4,13,（,4,13,9,19,1,）,=,4,9,19,1,=,2,10,19,=,8,9,19,（,2,2,8,+,4,1,8,+,5,8,）,=,8,9,19,7,=,1,9,19,3,8,在括号里填上哪个数，可以使计算简便？,+,（）,+1,3,8,+2,5,9,A.B.C.D.,5,8,5,9,5,8,4,9,5,8,5,5,13,（）,A.B.C.,5,13,8,13,3,8,1.,2.,B,D,我来试一试,+,+,+,1,9,5,9,7,15,8,15,3,1,4,1,3,+,同学们打印一篇作文，小红用了 分，小明比,小红多用 分，小军比小明多用 分，小军要,用多少时间？,7,1,3,10,7,+,7,8,1,+,7,10,=,7,3,10,+,7,10,（,）,+,1,7,8,=,8,+,1,7,8,=,9,7,8,（分）,答：,小军打印这篇作文要用 分。,9,7,8,耐心解一解,减去,3,的差再加上 ，结果,是多少？,3,5,6,7,细心看一看,1,7,8,3 +,1,7,3,5,6,7,=8 +,3,6,7,1,7,1,3,=9,3 =5,3,5,2,5,静心想一想,1,9,4,1,4,3.55,1,5,=4,1,9,(0.25+3.55+0.2),=4,1,9,4,=,1,9,