[求助]问一道GWD数学题

williamjia

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.

答案为什么选D?

(1)充分 我清楚   (2)怎么充分啊? N求出的不是整数啊?

帮忙看一下了