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题库 / Prep2007E2-DS-194
If r is the remainder when the positive integer n is divided by 7, what is the value of r ?
(1) When n is divided by 21, the remainder is an odd number.
(2) When n is divided by 28, the remainder is 3.
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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条件一：除以21之后，余数为奇数，有诸多可能性,j举例：n=22,24。26,28,30……，这些除以7的余数均不唯一
条件二：除以28之后，余数为3，那么除以7，余数肯定也为3
1) n = 21k+b (b is known as an odd number)
2) n = 28k +3