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题库 / GMATAdvanced-DS-62
If x and y are integers between 10 and 99, inclusive, is (x-y)/9 an integer?
(1)x and y have the same two digits, but in reverse order.
(2)The tens' digit of x is 2 more than the units' digit, and the tens' digit of y is 2 less than the umits' digit.
Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.
Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.
BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.
EACH statement ALONE is sufficient.
Statements (1) and (2) TOGETHER are NOT sufficient.
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这题的2很容易把1中限定为二位数的条件代入，但实际并不保证xy的位数是相同的，因此2很明显not sufficient
条件一：10a+b-(10b+a)=9a-9b=9(a-b)，满足条件
条件二：注意此时xy不再是have same digits，因此设第一个数为10a+b,第二个数为10c+d,a=b+2,c=d-2,联立之后算出来11b-11d+4，不能保证一定是9的倍数，因此排除
【11（α-β）+40】/9=integer