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Another tough question

by yumi2012 » Sun Aug 18, 2013 8:31 pm
Can't figure out the second question...

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Each senior in a college course wrote a thesis. The lengths, in pages, of those seniors' theses are summarized in the graph above.

a. What is the least possible number of seniors whose theses were within six pages of the median length?

b. What is the greatest possible number of seniors whose theses were within six pages of the median length ?


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by Brent@GMATPrepNow » Mon Aug 19, 2013 6:33 am
yumi2012 wrote: Image

Each senior in a college course wrote a thesis. The lengths, in pages, of those seniors' theses are summarized in the graph above.

a. What is the least possible number of seniors whose theses were within six pages of the median length?

b. What is the greatest possible number of seniors whose theses were within six pages of the median length ?
First determine the median thesis length. This seems a little tricky (since we have ranges for the thesis lengths), but we could still list the ranges in ascending order.
We get: (0-9),(10-19),(10-19),(10-19),(10-19),(20-29),(20-29),(20-29),(20-29),(20-29),(20-29)...

Since there are 20 papers altogether (1+4+6+7+2 = 20), the median will be the mean (average) of the 10th and 11th terms.
So, the median can have several possible values.

a. What is the least possible number of seniors whose theses were within six pages of the median length?
Here's one way to minimize this value:
{2,11,11,11,11,20,20,20,20,29,29,39,39,39,39,39,39,39,49,49}
Here, the median = (29+29)/2 = 29.
So, there were only 2 theses within six pages of the median length

a. What is the greatest possible number of seniors whose theses were within six pages of the median length?
IMPORTANT: If we make the median length right in the middle of the 20-29 range, then the theses in the ranges on either side will both be within 6 pages.
Here's what I mean.
{2,19,19,19,19,20,20,20,20,20,29,30,30,30,30,30,30,30,49,49}
Here, the median = (20+29)/2 = 24.5
So, there were 17 theses within six pages of the median length

Cheers,
Brent
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by yumi2012 » Mon Aug 19, 2013 2:21 pm
Thanks Brent ! But I still don't get how you got 17 for the second question. What's the relationship between 24.5 and answer 17?
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by Brent@GMATPrepNow » Mon Aug 19, 2013 4:30 pm
yumi2012 wrote:Thanks Brent ! But I still don't get how you got 17 for the second question. What's the relationship between 24.5 and answer 17?
In the scenario I provided, the median thesis length is 24.5 pages. In this scenario, 17 of the 20 theses were within six pages of the median length (of 24.5 pages)

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Brent
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by mikepamlyla » Tue Aug 20, 2013 8:47 am
Hi Brent,

Just curious how you obtained the values in the brackets for part A and B.

{2, 11, 11, 11, 11....}
{2, 19, 19, 19, 19....}

Thanks!
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