How many 3-digit positive intergers are odd and do not contain the digit 怎么算?请指教
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Howmany3-digitpositiveintergersareoddanddonotcontainthedigit怎么算?请指教Howmany3-digitpositiveintergersar
How many 3-digit positive intergers are odd and do not contain the digit 怎么算?请指教
How many 3-digit positive intergers are odd and do not contain the digit 怎么算?请指教
How many 3-digit positive intergers are odd and do not contain the digit 怎么算?请指教
先排除5所有可能在的地方
第一个数字可以是1,2,3,4,6,7,8,9里的任何数字.因此,有8种不同的方式来选择第一个数字.
第二位可以是0,1,2,3,4,6,7,8,9里的任何一个.因此,有9种不同的方法来选择第二个数字.
第三位数字应该是奇数.排除所有偶数和5后,第三位数字可以1,3,7,9里的任何一个.有4种不同的方法来选第三位.
因此,总共有8×9×4 = 288的方式
所有三位数的正整数,求其中一共有多少不包括数字5的奇数,你就数一数就行了
在3位的正整数当中有多少个不包含数字5的奇数?
解法:
个位数可选数字为:1、3、7、9,共4个
十位数可选数字为:0~9不包含5,共9个
百位数可选数字为:1~9不包含5,共8个
因此符合题意的奇数总数为:4x9x8=288个
不包含数字5的3位正奇数有多少个?
个位4种排法,百位8种排法,十位9种排法,共288种排法。
不包含数字5的3位正奇数有288个
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