苏教版五年级下册约分1市公开课一等奖百校联赛特等奖课件.pptx

苏教版五年级数学下册,约分,第1页,教学目标,1.深入了解分数基本性质；并能初步利用分数基本性质进行约分。,2.掌握约分含义和约分普通方法，学会约分书写形式，认识最简分数。,第2页,20,40,=,(),(),第3页,20,40,=,40,80,60,120,80,160,=,=,=,=,(),(),第4页,20,40,=,10,20,5,10,4,8,2,4,1,2,=,=,=,=,第5页,你能写出和 相等,而,分子、分母都比较小,分数吗?,12,18,第6页,12,18,122,182,6,9,=,=,6,9,63,93,2,3,=,=,第7页,12,18,6,9,=,2,3,=,把一个分数化成同它相等，,但分子、分母都比较小,分数，叫做约分.,第8页,12,18,6,9,2,3,=,2,3,第9页,12,18,2,3,=,2,3,第10页,分子和分母,只有公因数1，,这么分数叫做,最简分数。,约分时，通常要约成最简,分数。,第11页,1、下面哪些分数是最简分数,3,5,6,4,1,8,12,9,10,7,10,15,15,16,第12页,6,4,=,3,2,3,2,12,9,4,3,=,4,3,10,15,2,3,=,2,3,第13页,2、把下面各分数约分,10,12,12,15,15,25,35,21,60,45,40,90,第14页,10,12,5,6,=,2,3,12,15,4,5,=,4,5,第15页,15,25,3,5,=,3,5,35,21,5,3,=,5,3,第16页,60,45,20,15,=,4,3,4,3,60,45,4,3,=,4,3,第17页,40,90,4,9,=,4,9,40,90,20,45,=,4,9,4,9,第18页,把分数约分，重点要找准分,子和分母公因数，还要注,意书写形式。,第19页,分别说出下面各分数分子和,分母有没有公因数2、5、3。,9,15,25,35,14,42,30,36,45,15,18,51,第20页,9,15,25,35,14,42,30,36,有公因数3,有公因数5,有公因数2、7,有公因数2、3,第21页,45,15,18,51,有公因数3、5,有公因数3,第22页,把下面没有约成最简分数约成最简分数。,12,18,6,9,=,28,32,7,8,=,42,24,21,12,=,52,78,26,39,=,第23页,12,18,6,9,=,42,24,21,12,=,52,78,26,39,=,=,2,3,=,7,4,=,2,3,第24页,把相等分数连起来。,20,28,42,49,15,9,24,30,28,42,13,39,1,3,4,5,5,7,5,3,2,3,6,7,第25页,把下面各分数约分。,16,20,18,15,22,33,36,63,18,54,45,60,80,48,第26页,18,15,22,33,18,54,45,60,80,48,16,20,=,4,5,=,6,5,=,2,3,=,1,3,36,63,=,4,7,=,3,4,=,5,3,第27页,把下面各分数约分。,16,20,18,15,22,33,36,63,18,54,45,60,80,48,第28页,