Statistics

Question

How many integers lie between the mean and the Standard deviation?

Given 25,30,35,40,45.

Bunuel · Answer

This is not a GMAT type of question plus it has very poor and ambiguous wording.

If the question is:  how many of the 5 listed data points are within 1 standard deviation of the mean  then the answer will be 3: mean=35 and SD=~7, so there are 3 data points from  mean-SD=35-7=28  to  mean+SD=35+7=42 , namely: 30, 35, and 40.

144144 · Answer

how do u calculate the sd?

CompetitiveAaron · Answer

Hi Bunnel,

Is the SD not 5?

Bunuel · Answer

Again: this is not a GMAT type of question, plus it has very poor and ambiguous wording. So, I wouldn't worry about it at all. Anyway: you won't be asked to actually calculate the standard deviation of a set on the GMAT. You just need to understand the concept of it: standard deviation shows how much variation there is from the mean, how widespread a given set is. So, a low standard deviation indicates that the data points tend to be very close to the mean, whereas high standard deviation indicates that the data are spread out over a large range of values. Check this for more: math-standard-deviation-87905.html PS questions on SD: ps-questions-about-standard-deviation-85897.html DS questions on SD: ds-questions-about-standard-deviation-85896.html No, SD=\sqrt{50} . check the above links for more.

fluke · Answer

25,30,35,40,45.

mean = 25+45/2=70/2=35

\sigma^2 = \frac{(25-35)^2+(30-35)^2+(35-35)^2+(40-35)^2+(45-35)^2}{5} 
 \sigma^2 = \frac{100+25+0+25+100}{5} 
 \sigma^2 = \frac{250}{5} 
 \sigma^2 = 50 
 \sigma = \sqrt{50} \approx 7

where  \sigma  is standard deviation.

How many integers in the dataset are within 1 std dev about the mean=35

Minimum= 35-7=28
Maximum= 35+7=42

Ans: 3 (30, 35 and 40)

CompetitiveAaron · Answer

Thanks Bunuel and Fluke.. +1 kudos to you both

144144 · Answer

Fluke - great work. +1

bumpbot · Answer

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