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Re: DS questions about standard deviation
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10 Jun 2017, 10:13

sasidharrs wrote:

2. What is the standard deviation of Q, a set of consecutive integers? (1) Q has 21 members. (2) The median value of set Q is 20.

Hi Banuel, I have a question on the the above SD, Everyone is saying answer is A, But, The question itself is giving the answer without need of choices, coz, he gave a set of consecutive integers, which means SD is 1. You cannot assume all are different or all are same. I don't need 1 or 2 to decide it right?

Can you please explain me.

No, that's not correct. Sets with different number of elements will give different standard deviation. The SD of {1, 2} is different from that of {1, 2, 3, 4, 5, 6}
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DS questions about standard deviation
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29 Oct 2017, 16:25

3. Lifetime of all the batteries produced by certain companies have a distribution which is symmetric about mean m. If the distribution has a standard deviation of d , what percentage of distribution is greater than m+d? (1) 68 % of the distribution in the interval from m-d to m+d, inclusive (2) 16% of the distribution is less than m-d

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29 Oct 2017, 20:31

radhikakhemka007 wrote:

3. Lifetime of all the batteries produced by certain companies have a distribution which is symmetric about mean m. If the distribution has a standard deviation of d , what percentage of distribution is greater than m+d? (1) 68 % of the distribution in the interval from m-d to m+d, inclusive (2) 16% of the distribution is less than m-d

Can you please explain the solution of this question? How are both statements Sufficient?

The lifetime of all the batteries produced by a certain company in a year have a distribution that is symmetric about the mean m. If the distribution has a standard deviation of d, what percent of the distribution is greater than m+d?

Symmetric about the mean means that the shape of the distribution on the right and left side of the curve are mirror-images of each other.

(1) 68% of the distribution lies in the interval from m-d to m+d, inclusive --> 100%-68%=32% is less than m-d and more than m+d. As distribution is symmetric about the mean then exactly half of 32%, or 16%, would be more than m+d. Sufficient.

(2) 16% of the distribution is less than m-d --> again, as distribution is symmetric about the mean then exactly 16%, will be more than m+d. Sufficient.