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题库 / GMATAdvanced-DS-72
If K is a positive integer less than 10 and N=4, 321+K, what is the value of K?
(1)N is divisible by 3.
(2)N is divisible by 7.
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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N=4321+K
sum of digits of N = 4+3+2+1 = 10
so K can be 2,5 or 8 to make N divisible for 3.
Not sufficient.
If we divide 4321 by 7, we get the remainder of 2. To make N divisible 7, K must be 5, since K is a positive integer less than 10.
sufficient.
B
不把条件一的限制条件，代入条件二的求解中！！！
条件二：直接算4321/7，可得余数是2，说明要整除7，还需加5，则K=5，唯一，条件充分
一个整数的个位数字去掉，并用剩下的数减去这个个位数字的2倍得到的数如果是7的倍数那么这个数便可以被7整除