if k is a positive integer and the tens digit of k + 5 is 4, what is the tens digit of k?
1. k>35 2. the units digit of k is greater than 5.
k+5的十位数是4,那么k的十位数有可能是3,也有可能是4. k介于35和44之间。
(1)知道k大于35,没用
(2)k的个位数大于5,那么k应该在36到39之间,可以判断十位为3.
1,因为不代表什么.大于35可是是36也可以是40,41OR ANYTHING..
2,各位大于5,大于5加5一定就要进位了,所以加法之前的十位数应该是3.
选B.
个人算法,错了不要打我哦.
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