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ds - word problem

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Master | Next Rank: 500 Posts
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by ccassel » Tue Apr 05, 2011 6:23 pm
Hi,

How would you explain the answer to this question?

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

Cheers,
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Source: — Data Sufficiency |
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by vineeshp » Tue Apr 05, 2011 6:36 pm
OA is D.

From 1st , 500n = (1/16)(500n + 500 n^2) Can be solved for n

From 2nd, 500n + 500 n^2 = 120000 , can be solved for n.

Hence D
Vineesh,
Just telling you what I know and think. I am not the expert. :)
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by MAAJ » Tue Apr 05, 2011 6:51 pm
Edit: Oh yeah, statement 1 is sufficient :p

IMO [spoiler](D)[/spoiler]

My Math formula for this:

Draw 2 sticks, for each stick draw 2 more
This equal a total of 2 + 4 sticks

Draw 3 sticks, for each stick draw 3 more
This equal a total of 3 + 9 sticks

So the formula here is n + n^2 to get the number of people
Now to get the amount of money we must multiply by 500:
500n + 500n^2 = Total Money

1) tell us that 500n = 1/6 * (Total Money)
500n = 1/6 (500n + 500n^2) can be solved for n

2) give us the "Total Money" so if we apply the formula we get:
500n + 500n^2 = 120,000 -> which is a Quadratic equation that can be solved for n.

ccassel wrote:Hi,

How would you explain the answer to this question?

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

Cheers,
"There's a difference between interest and commitment. When you're interested in doing something, you do it only when circumstance permit. When you're committed to something, you accept no excuses, only results."
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by ccassel » Wed Apr 06, 2011 7:51 am
That is great. Thanks.

I was trying to plug in and work backwards but with quadratic equations it proves very difficult.

Cheers,
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