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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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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.
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