Each of the 4 students in a certain class read several books during th

sd is the measure of the dispersion of the dataset relative to its mean; if all datapoints are the same, the sd=0, if not, then the sd>0; the greater the difference between datapoint and the mean the greater the sd, and the closer the datapoint is to the mean, the smaller the sd.

(1) The range of the number of books read by the 4 students during the past month was 0. sufic

range=0 then, all datapoints are equal, thus sd=0.

(2) One of the 4 students read 5 books during the past month. insufic

s1: 5, but the others are unknown.

Ans (A)

(1) The range of the number of books read by the 4 students during the past month was 0. That means there would be no deviation (or standard deviation =0).
SUFFICIENT

(2) One of the 4 students read 5 books during the past month.
We don't know how many books read by each of the other three students.
NOT SUFFICIENT.

FINAL ANSWER IS (A)

Posted from my mobile device

1.The range is the highest number minus the lowest; if the range is 0 therefore all the numbers are the same meaning the sd is also 0
Sufficient
2. We don’t know the other numbers
Insufficient

Therefore
A

Posted from my mobile device

#1
The range of the number of books read by the 4 students during the past month was 0.
means all value are equal or say identical so the SD would be 0 as well ; sufficient
#2
One of the 4 students read 5 books during the past month.
other students books info not know ; insufficient
IMO A



Each of the 4 students in a certain class read several books during the past month. What was the standard deviation of the numbers of books read by the 4 students during the past month?

(1) The range of the number of books read by the 4 students during the past month was 0.

(2) One of the 4 students read 5 books during the past month.

Four students read some books within the previous month. We are to determine the SD of the books read by the four students.

Statement 1: The range of the number of books read by the 4 students during the past month was 0.
From statement 1 above, we can conclude that the four students read the same number of books in the previous month since the range is 0. And once the range is zero, it means that the standard deviation is 0 as well. Statement 1 is sufficient.

Statement 2: One of the 4 students read 5 books during the past month.

Clearly insufficient. The remaining three students could each read 5 books as well in which case the SD is zero. They could each read 6 books or any number of books different from 5 in which case SD is not zero.

The answer is A.

Posted from my mobile device

1) Sufficient :If the range is zero, then all of the numbers are the same and the standard deviation is zero.

2) Insufficient

A

It is Gmat prep question
Please tag

Dear Bunuel ,

Please tag the question - GMATPREP - EP6

Best !!

________________________
Done. Thank you.

(1) When range is 0, which means all 4 number were equal, and the standard deviation will be 0. Sufficient.

(2) No information of other three. Insufficeint.

The answer is A.

I actually encountered this problem while I was doing exam prep #5.

The first option says that range is 0 and that means Max - Min = 0, not all four of them have difference of zero, no?

iow, if we assume that a<b<c<d

and d-a = 0, how about b and c?

cuz of that I have selected E. The first option does not explicitly say that difference between every number is zero, but only max-min

janbol, if the highlighted portion is true. D-a cannot be 0 as D would be greater than a.

If max-min = 0, then all the numbers would be equal. Think about it, all the values would fall between max and min, if the max and min are same, that does not leave any space for the remaining values. They'd have to be equal to max and min.

If this doesn't help, try thinking of an actual number set (not variables) in which the range is 0, but the numbers are different.

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