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GWD管卫东GMAT 第7套题
If x is a positive integer,is theremainder 0 when 3^X + 1 is divided by 10?(X是指数,我电脑表示不出来)
(1) x = 4n + 2,where n is apositive integer.
(2) x> 4
A.Statement (1) ALONE is sufficient,but statement (2) alone isnot sufficient.
B.Statement (2) ALONE issufficient,but statement (1) alone is not sufficient.
C.BOTH statements TOGETHERare sufficient,but NEITHER statement ALONE is sufficient.
D.EACH statement ALONE issufficient.
E.Statements (1) and (2)TOGETHER are NOT sufficient.
想不通啊
人气:322 ℃ 时间:2020-06-03 21:20:33
解答

7-Q11:

x是正整数

问:[(3^x)+1]/10的余数是否为0?


statement (1): x = 4n + 2,其中n是正整数

3^x的个位数即为(3^x)/10的余数

由上表可知,3^x的个位数的周期为4,即(3^x)/10的余数的周期为4

因此,x=4n+2时,(3^x)/10的余数为9, [(3^x)+1]/10的余数为0,SUFF


statement (2): x>4, [(3^x)+1]/10的余数有多种可能,INSUFF


选A

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