9×19×29×39·····×2009的个位数是几?

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9×19×29×39·····×2009的个位数是几?
9×19×29×39·····×2009的个位数是几?

9×19×29×39·····×2009的个位数是几?
每100个数有10个个位为9的每1000个数包含10个100
所以1000里面有100个个位为9的
一共是2*100+1=201
9*9=81 1*9=9 9*9=81
所以每两个9相乘个位就为1
所以201包含100对,外加一个单独的2009
所以个位肯定为9

先算出有几个9
(2009-9)/10=200
200+1=201
有201个9
9相乘后，个位数字以 9 1 9 1 循环
因为有201个9，所以个位数字会是9

9×19×29×39·····×2009由9-99共10个数，同理得109-199也是10个数，。。。。。1909-1999也是10个数，然后最后还有一个2009，所以这么多个数总数为奇数，个位都是9偶数个9相乘为1所以，9×19×29×39·····×1999的个位数为1，那么再乘以一个2009，个位数为9。
所以9×19×29×39·····×2009的个位数是9...

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