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Brian is analyzing the performance of certain stocks. He finds that

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New post 14 Jul 2011, 12:09
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Brian is analyzing the performance of certain stocks. He finds that for the first fifteen days of a 30 day period, the daily closing price per share of Phonexpharma Inc. conformed to the function \(f(x)=0.4x+2\) , where x represents the day in the period. He found that for the last 15 days in the same period, the stock followed the function \(f(x)=(-1/7)x+9\), where x represents the day in the period. Approximately what is the median closing price per share of Phonexpharma Inc. for the entire 30 day period?


4.7

5.55

6.71

8

11.1


Is it possible to get such questions on the actual exam :( If so, what is the best way to go about it?
[Reveal] Spoiler: OA

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New post 14 Jul 2011, 12:38
For first 15 days: F1
For last 15 days: F2
Median is (15th day value + 16th day value)/2
15th day value : substitute x=15 in F1
16th day value : substitute x=1 in F2

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New post 14 Jul 2011, 13:04
piyatiwari wrote:
For first 15 days: F1
For last 15 days: F2
Median is (15th day value + 16th day value)/2
15th day value : substitute x=15 in F1
16th day value : substitute x=1 in F2


I do not think that will provide the right answer. I get ~ 8.5 as the median using your inputs. However, it is 5.5.

Guess the imp thing is that the median is not value on 15/16th day value but 15/16 values in ascending order.

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First 15 days: F1, x= 1 to 15 and f(x)= 2.4 to 8
Last 15 days: F2, x= 16 to 30 and f(x) = ~4.7 to ~6.7 (30th to 16th)

Median is average of 15th and 16th value when all of the above values are arranged in order

Do not try to calculate all the values. Go for the choices.

11.1 - outside the range of values
8- last value
6.71 - last value for the F2, so already we have 15 values less than 6.71. Additionally F1 has some values less.
4.7 - First value for the F2, so already we have 15 values greater than 4.7. Additionally F1 has some values greater.

Hence 5.55 must be the answer.

If we had very close answer choices, it would have been very calculation- intensive problem.
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New post 15 Jul 2011, 18:34
as i understood, the median of 30 days is the (fifteenth day + the sixteenth day )/2
and i dont get the answer you gave :(. i found 7.5

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New post 15 Jul 2011, 18:39
ohh right! from 1 to 15 days, the biggest number is 8
from 16 to 30 then smallest number is 4.27
so the median is 6.1 and 6.1 is between 5.5 to 6.5
maybe b is the answer

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New post 16 Jul 2011, 02:28
good question. Thanks Hellishbrain for sharing the solution! so, for median calc in such questions, we get the range from each function first and then eliminate answer choices. if cant eliminate, then we have to make a guess and move on since it looks very calculation intensive to find out the 15-16 values in the order.
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New post 06 Sep 2017, 13:47
If I am not mistaken, I don't think we need to make any guesses once we have calculated the highest and the lowest values from each of the first and last 15 days.

Highest (First 15 days) = 8
Smallest (First 15 days) = 2.4

Highest (Last 15 days) = 6.72
Lowest (Last 15 days) = 4.72

Median is the middle value of the set when all values are arranged in the ascending order. We know 4 values from the set of 30 and arranging them would look something like:

2.4 ---- 4.72 -- Median -- 6.72 ---- 8

Median is approximately between 6.72 and 4.72. Only Option B - '5.55' satisfies that.

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Re: Brian is analyzing the performance of certain stocks. He finds that   [#permalink] 06 Sep 2017, 13:47
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