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题库 / Prep2007E1-DS-211
If k is a positive integer, then 20k is divisible by how many different positive integers?
(1) k is prime.
(2) k = 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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注意是多少个different positive integers，如果是how many positive integers？那只要k是个质数，因数的个数=2(1和本身)+C(4,3)+C(4,2)+C(4,1)是固定的。
问different positive integer，要考虑p是否等于2或5.
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