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题库 / Prep2007E1-DS-157
If n is a positive integer and r is the remainder when 4 + 7n is divided by 3, what is the value of r ?
(1) n + 1 is divisible by 3.
(2) n > 20
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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4+7n=7(n+1)-3
条件一：n+1能被3整除，则4+7n=7(n+1)-3肯定能被3整除：前面有个7（n+1）可以被3除，再减去一个3，变6？，充分；
条件二：n>20,4+7n还是各种不确定，不充分；