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# Is the standard deviation of prices (per share) of 10 stocks less than

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Joined: 29 Jan 2015
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WE: General Management (Non-Profit and Government)
Is the standard deviation of prices (per share) of 10 stocks less than  [#permalink]

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Updated on: 12 Jan 2019, 03:40
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Difficulty:

45% (medium)

Question Stats:

58% (01:13) correct 42% (00:53) wrong based on 45 sessions

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Is the standard deviation of prices (per share) of 10 stocks less than $50? (1) The highest price is$80, and the lowest price is $50. (2) The average of price of the 10 stocks is$60.

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Originally posted by rohan2345 on 11 Jan 2019, 06:02.
Last edited by Bunuel on 12 Jan 2019, 03:40, edited 1 time in total.
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Joined: 01 May 2017
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Re: Is the standard deviation of prices (per share) of 10 stocks less than  [#permalink]

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11 Jan 2019, 20:07
Is the standard deviation of prices (per share) of 10 stocks less than $50? (1) The highest price is$80, and the lowest price is $50. Highest and Lowest price are given, implies range = 30$
All the prices of remaining stocks lie with in the range and the mean as well
50 < mean < 80

standard deviation = $$\sqrt{Sum of((x- mean))^2/10}$$

(x-mean) < 30
Let us consider the extreme case,
Sum of all (x-mean)^2 < (10*(30)^2)/10 < (30)^2
Taking square root of 30^2 gives the standard deviation, which is always less than $50 Sufficient (2) The average of price of the 10 stocks is$60.
We have no idea of the 10 stock prices, they may vary by high difference making standard deviation > 50 or vary by very less difference making standard deviation < \$50
Insufficient

Option A is correct
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Re: Is the standard deviation of prices (per share) of 10 stocks less than  [#permalink]

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12 Jan 2019, 10:26
Yes, is this an official question? I doubt that they would ask to find the value of a standard deviation, and even more if the SD is so big given the range.
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Re: Is the standard deviation of prices (per share) of 10 stocks less than   [#permalink] 12 Jan 2019, 10:26
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