I think, metallicafan wants to validate his logical reasoning in this case. Therefore, here are my 2 cents on this question.
When I did this question, the first question that came in my mind is - What could be the value, which I was assuming, of Standard Deviation. Then, I rechecked the question I found out is value of std deviation should be positive. i.e. no zero and no negative is allowed.
Assume d to be minimum i.e "1" and see the impact of expected data sets on the mean and std deviation, by using the definition and concept that Bunuel provided.
example - Take choice A . 80 and 80, since you have assumed the d to be 1, therefore, adding these two values will increase the mean and hence standard deviation. Therefore, incorrect.
Remember, your task is to stay close to the mean.
Now, check the impact of each n every choice.
Thanks
H
metallicafan wrote:
A certain list of 200 test scores has an average (arithmetic mean) of 85 and a standard deviation of d, where d is positive. Which of the following two test scores, when added to the list, must result in a list of 202 test scores with a standard deviation less than d ?
(A) 80 and 80
(B) 80 and 85
(C) 80 and 90
(D) 85 and 85
(E) 85 and 90
Intuitively, I can see that the answer is the OA. However, can we be sure that the other choices don't reduce the size of the standar deviation?
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