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by dunkin77 » Thu Jun 14, 2007 11:10 am
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 1/16 of the total amount donated.
(2) The total amount donated was $120,000.



Hi,
I thought the answer was B but OA is D -- Can anyone explain how to get n from 1)??

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by simplythebest » Fri Jun 15, 2007 5:13 am
It is D.

1. 500n = 1/16[500(n)(n+1)]
16*500n = 500(n)(n+1)

divide both sides by 500(n)

16 = n+1 and hence n=15


2. 500(n)(n+1) =$120,000

n^2+n-240=0 = n^2+16n-15n+240 = 0 (n cannot be negative) and hence n will be 15.

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by dunkin77 » Fri Jun 15, 2007 9:38 am
Thank you.

One question.

500n*(n+1) .. is +1=Mary?

I was thining 500( n*n)...