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,第,2,课时,3,的倍数的特征,R,五年级下册,第 2 课时 3 的倍数的特征R五年级下册,117,是,2,的倍数吗？,是,5,的倍数吗？,个位,上是,0,、,2,、,4,、,6,、,8,的数是,2,的倍数,个位,上是,0,或,5,的数是,5,的倍数,2,、,5,的倍数为什么只与,个位,有关呢？,117是2的倍数吗？是5的倍数吗？个位上是 0、2、4、6、,117,1002,50,102,5,1171002501025,117,1005,20,105,2,1171005201052,几个,10,个位,十位,百位,千位,几个,100,几个,1000,2,、,5,的倍数,6,5,9,几个个位十位百位千位几个几个2、5 的倍数659,思,考,3,的倍数特征,会不会只与,个位,有关呢？,思考3的倍数特征会不会只与个位有关呢？,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,91,92,93,94,95,96,97,98,99,100,（,1,）上表中哪些是,3,的倍数？把它们圈起来。,123456789101112131415161718192,3,6,9,12,15,18,21,24,27,30,33,36,39,42,45,48,51,54,57,60,63,66,69,72,75,78,81,84,87,90,93,96,99,（,2,）横着看，圈起来的前,10,个数，个位分别是哪些数字。,3,6,9,2,5,8,1,4,7,0,369121518212427303336394245485,3,6,9,12,15,18,21,24,27,30,33,36,39,42,45,48,51,54,57,60,63,66,69,72,75,78,81,84,87,90,93,96,99,（,2,）判断一个数是不是,3,的倍数，只看个位行吗？,3,6,9,2,5,8,1,4,7,0,不行,3,的倍数个位上可以是任意数。,369121518212427303336394245485,3,6,9,12,15,18,21,24,27,30,33,36,39,42,45,48,51,54,57,60,63,66,69,72,75,78,81,84,87,90,93,96,99,（,3,）斜着看，你发现了什么？,369121518212427303336394245485,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,91,92,93,94,95,96,97,98,99,100,斜着看，,3,的倍数各位上的数的和都是,3,的倍数。,123456789101112131415161718192,任意找几个,3,的倍数，把各位上的数相加，看看你有什么发现？,42,4+2=6,，,6,是,3,的倍数,78,7+8=15,，,15,是,3,的倍数,一个数各位上的数的和是,3,的倍数，这个数就是,3,的倍数。,任意找几个3的倍数，把各位上的数相加，看看你有什么发现？42,归纳小结,2,的倍数：个位是,0,、,2,、,4,、,6,、,8,5,的倍数：个位是,0,、,5,3,的倍数：各位上数字之和是,3,的倍数,归纳小结2 的倍数：个位是 0、2、4、6、85 的倍数：个,117,1003,331,103,31,1+1+7,9,3,的倍数,1171003331103311+1+79,127,1003,331,203,62,1+2+7,10,不是,3,的倍数,1271003331203621+2+71,下面用数字卡片摆出的数字中哪些是,3,的倍数？在每个数后面增加一张卡片，使这个三位数成为,3,的倍数。,2,4,5,8,2+4=6,24,是,3,的倍数,0,3,6,9,5+8=13,58,不是,3,的倍数,2,5,8,下面用数字卡片摆出的数字中哪些是3的倍数？在,4,7,9,6,4+7=11,47,不是,3,的倍数,1,4,7,9+6=15,96,是,3,的倍数,0,3,6,9,47964+7=111479+6=150369,智慧屋,智慧屋,1.,圈出,3,的倍数。,92 75 36 206 65 3051 779 99999,111 49 165 5988 655 131 222 7203,像,99999,、,7203,这么大的数，你是怎么判断的？,7203,中先把,3,和,0,划去，剩下的,7,2,9,，是,3,的倍数，所以，这个数是,3,的倍数。,这种方法叫,“弃,3,”法,，就是先把,3,的倍数划去，剩下的数再相加判断。,1.圈出3的倍数。92 75 36,2.,在,里填一个数字，使每个数都是,3,的倍数。,7,4,2,44,65,12,1,2,5,8,0,3,6,9,1,4,7,1,4,7,2,5,8,2.在里填一个数字，使每个数都是3的倍数。7,3.,下面的判断正确吗？小组间相互讨论一下。,（,1,）个位上是,3,、,6,、,9,的数，都是,3,的倍数。,（,2,）奇数都不是,3,的倍数。,（,3,）是,9,的倍数的数，一定是,3,的倍数,。,3.下面的判断正确吗？小组间相互讨论一下。（1）个位上是,4.,从下面,4,张数字卡片中取出两张组成两位数，要求分别满足下面的条件：,4,3,0,5,（,1,）是,3,的倍数,（,2,）同时是,2,和,3,的倍数,30,45,54,30,54,4.从下面 4 张数字卡片中取出两张组成两位数，要求分别满,4.,从下面,4,张数字卡片中取出两张组成两位数，要求分别满足下面的条件：,4,3,0,5,（,3,）,同时是,5,和,3,的倍数,（,4,）同时是,2,、,3,、,5,的倍数,30,45,30,4.从下面 4 张数字卡片中取出两张组成两位数，要求分别满,
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