,第9课时 找最小公倍数,北师大版五年级上册,新课导入,问题：,谁能举例说说,4,的倍数？,6,的倍数呢？,4,的倍数有,4,，,8,，,12,，,16,6,的倍数有,6,，,12,，,18,，,24,为什么在说倍数时要加省略号呢？,推进新课,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,你能在上表中分别找出,4,和,6,的倍数吗？,问题：,用“”标出,4,的倍数，用“”标出,6,的倍数。,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,哪些数上既标有“”又标有“”？,两种标记都有的数有,12,，,24,这些数有什么特点呢？,它们既是,4,的倍数，也是,6,的倍数。,在数学上把这些数都叫做,公倍数。,在这些公倍数中，有没有最大公倍数呢,?,几个数相同的倍数叫作这几个数的,公倍数,。,问题：,总结一下什么叫公倍数？,12,就是,4,和,6,的最小公倍数。,4,和,6,的公倍数有,。,4,和,6,的最小公倍数是,。,12,，,24,，,36,，,48,12,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,4,的倍数,6,的倍数,12,24,8,，,4,，,18,，,6,，,30,，,4,和,6,的公倍数,12,24,问题：,淘气用下面的方法表示公倍数，你能看懂吗？,16,，,20,，,公倍数和最小公倍数的意义：几个数相同的倍数叫作这几个数的公倍数，其中最小的一个叫作这几个数的最小公倍数。,找公倍数的方法：先列举出几个数的倍数，再找出他们的公倍数和最小公倍数。,归 纳 小 结,1.,在下表中用“”标出,3,的倍数，用“”标出,5,的倍数。,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,随堂练习,哪些数上既标有“”又标有“”？这些数有什么特点？,15,30,45,。,它们都是,3,和,5,的公倍数。,2.,1,2,3,4,5,6,7,8,9,10,8,8,16,6,6,12,50,以内,6,和,8,的公倍数有,，,最小公倍数是,。,24,32,40,48,56,64,72,80,18,24,30,36,42,48,54,60,24,，,48,24,3.,想一想，填一填。,6,和,9,的最小公倍数是多少？,18,，,36,6,12,24,30,42,48,9,27,45,4.,求下面各组数的最小公倍数。,3,和,6,8,和,10,2,和,7,6,和,10,6,40,14,30,18,24,2,9,12,3,4,3,