gwd 19-10 math

Q10:

If $1,000 will be deposited in a bank account and I is the dollar amount of interest earned from the original deposit, represented as I = 1000 {(1 + r/100)ⁿ – 1}, and the annual interest rate is r percent, is r > 8 percent?

(1)   The deposit earns a total of $210 in interest in the first 2 years.

(2)     (1 + r/100)² > 1.15

A. Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.

B. Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.

C. BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.

D. EACH statement ALONE is sufficient.

E. Statements (1) and (2) TOGETHER are NOT sufficient.

key: D. But I think it is B. condition (2) cannot prove that r>8.

支持condition (2) cannot prove that r>8.either r>8 or r<8

所以答案为A

题目是问 if r>8% 即 if r>0.08 ，不是8哦。从这点看（2）条件也满足。选D

MM，题目已经说了8 percent,所以我就直接省略了，其实意思就是8%。

还是认为不应选D,因为条件（2）解出r为7.几%,无法判定r>0.08.只能作为必要条件，不是充分条件。

而题目意思是要求充分条件。所以（2）是不正确的

首先谢谢hitlzc及时的回复, 我可能没有表达清楚自己的意思，再说明一下：

条件（2）解出r为7.几，不是7.几% ，所以既然r>7.几，就必然r>8%=0.08，如果题目问的是is r >8，那么（2）就不正确了，现在题目是问 is r>8%，所以条件（2）成立。选D。

七楼的也有道理, 题目问的是 is r>8 percent? 也就是r是否大与0.08

题目中的r/100表示r%, 那么按七楼的意思就是这题目是问r是否大于0.008啦?

如果是这样自然选D, 但是这样一来又有什么意义呢?

所以是不是题目错啦啊? 应该是is r>8, 没有percent呢?