GWD数学一题

kgbht · 发表于 2010-3-18 15:15:04

请帮忙看条件二是否可以？多谢

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.

yawgamoth86 · 发表于 2010-3-18 16:07:46

可以啊
2: 500n + 500n^2 = 120000
500n (1+n) = 120,000
n (n+1) = 240
n = 15
話說您的第一個條件還少了一個數字1／6
順便給你1的
1: 500n = 1/16 (500n + 500n^2)
16 x 500n = 500n (1+n)
16 = 1+n
n = 15

kgbht · 发表于 2010-3-18 17:25:46

多谢啊！我脑袋短路啦。

GWD数学一题

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