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题库 / GMATAdvanced-DS-8
For each positive integer k, let ak =(1+~$\frac{1}{k+1}$~ )Is the product a1,a2...an an integer?
(1)n+ 1 is a multiple of 3.
(2)n is a multiple of 2.
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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带入消数字剩下（n+3）/2对圈一，可为3可为6整个式子奇偶不确定，对于圈二是确定答案所以b
不是n+2/2 么
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for n=1, a1= 3/2
for n=2, a2= 4/3
for n=3, a3= 5/4
for n=4, a4= 6/5
Testing products:
n=even, product is an integer (a1*a2= 2 , a1*a2*a3*a4= 3)
n=odd, product is a non-integer (a1*= 3/2 , a1*a2*a3= 5/2)
St1: n+1 as a multiple of can be either odd or even and hence n can be either as well. Insufficient
St2: n is even. Sufficient.
整理式子，a1...an的乘积=(n+2)/2,题目要求是否为整数，即要求n+2是否为2的倍数，即n是否为偶数；条件1中，当n+1=6时，n=5,则不满足要求，条件2满足，选B
b