再请教一道GWD 1-11

whitecloud

Q11:

Mary persuaded n friends to donate $500 each to her election campaign, and then each of these n friends persuaded n more people to donate $500 each to Mary’s campaign. If no one donated more than once and if there were no other donations, what was the value of n?

(1) The first n people donated of the total amount donated.

(2) The total amount donated was $120,000.

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

答案给的是D,可我怎么都觉得是C, The number of the friends can't be calculated as n(n+1), because some friends may introduce same people(I think that's the reason why ets specifiy "no one donated more than once".

thanks!

robert

答案是D

总共denote 500n+n*n*500=500n(n+1)

1）500n知道，所以n可以求出

2）500n(n+1)=120000

n有两个解，但有一个是负数，所以n唯一

n

sammen

对于条件1我还有点问题，不太明白，什么数字都美给怎么定啊？请谁给说说。

mikejia

条件1给出" The first n people donated 1/16 of the total amount donated."

sammen

呵呵，谢谢啦。