Lesson: More Standard Deviation

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Hi Brent ,
These videos are great and very helpful. I was faced with same problem m+d one unit above/below the mean and i was able to tackle the question within a min. Thank you so much these videos are straight up to the point.

Thanks again !!!!
gmat-admin's picture

Hi Laxmi,
Thanks for taking the time to say that!

Perfect explanation and I save time

Hello Brent,

Can you please help me with the below question ?

What is the standard deviation of a set of numbers whose mean is 20?

(1) The absolute value of the difference of each number in the set from the mean is equal

(2) The sum of the squares of the differences from the mean is greater than 100

Since the absolute value of difference of each number from mean is equal, SD must be zero. I selected A as answer.

Thank you,
gmat-admin's picture

Good question.

Notice that the sets {-1, 1} and {-500, 500} both have a mean of 0, and the difference of each number in the set from the mean is equal. HOWEVER, the standard deviation in the 2nd set is much greater than the standard deviation in the 1st set

There are some nice solutions here: http://www.beatthegmat.com/what-is-the-standard-deviation-of-a-set-of-nu...


Pls help with the following question (will be helpful if you can highlight the concept that has been applied to the question):

A certain characteristic in a large population has a distribution that is symmetric about the mean m. If 68 percent of the distribution lies within one standard deviation d of the mean, what percent of the distribution is less than m + d ?

(A) 16%
(B) 32%
(C) 48%
(D) 84%
(E) 92%
gmat-admin's picture


Could you help me with the exercise #392 of OG17.

gmat-admin's picture

You bet, Pedro.

Here's my solution: https://gmatclub.com/forum/beginning-in-january-of-last-year-carl-made-d...


Thanks Brent!


Hi Brent, the following question is seeming to be tricky? I understand that there won't be any value besides the mean itself and as per my understanding of the question, it asks for the number of integer values within 3 units of SD of the mean. My answer - A) ZERO

A Bell Curve (Normal Distribution) has a mean of − 1 and a standard deviation of 1/8 . How many integer values are within three standard deviations of the mean?

A. 0
B. 1
C. 3
D. 6
E. 7
gmat-admin's picture

Hi Jalal,

The correct answer is B (1).
Given the above information, the values within 3 standard deviations of the mean are all values from -1 3/8 to -5/8 inclusive.
So, the integer -1 is within this range.

Here's my full solution: https://gmatclub.com/forum/a-bell-curve-normal-distribution-has-a-mean-o...


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