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Change in Std Dev when a new number is added

Problem Solving — algebra and arithmetic (GMAT Focus Edition)
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Source: — Quantitative Reasoning |
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by zenithexe » Sun Jul 12, 2009 5:50 pm
1. same as mean,
mean is same, Stdev is lower (how much lower will depend on the population size)

2.Greater than mean
mean is greater, stdev will be greater of lower depending on how close the new number is close to mean (ie if the new number X is mean<X<mean+SD the SD will be lower, but that's not always the case, it depends on the total number of samples, the characteristics..etc)
so SD can be lower or higher, it depends

well, that's what I gathered. There maybe perfect explanation about this somewhere on internet

3.Lower than mean
same thing, lower mean, but SD will depend on the characteristic of the sample population


I hope this helps
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