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Re: Mary persuaded n friends to donate $500 each to her election [#permalink]
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.

Amount donated by first n = 500 *n

Total Amount donated = 500 * n^2

1. 500n = 1/16 * 500 * n ^2
or n ^ 2/n = 16 or n =16

2. 500* n^2 = 120000


my answer is D as we can find n, however in 2nd case n does not come out to be a natural number.
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Re: Mary persuaded n friends to donate $500 each to her election [#permalink]
D would still be the answer
1- has been demonstrated by practicemore
2- 500n^2 + 500n = 120,000$
The first 500n^2 accounts for the "friends of friends" without accounting for the first n friends which is accounted for by adding 500n
You then have 500n(n+1) = 120,000
n(n+1) = 240
Only positive integer that fits is n=16



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Re: Mary persuaded n friends to donate $500 each to her election [#permalink]
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