standard deviation princeton manal

I have seen this question In Princeton Review mannual Pls advcice on same. Or let me know if it is requeired to ignore.

Anurag@Gurome wrote:

alltimeacheiver wrote:If the mean on this exam is 530, and the standard deviation (sd) is
110, what percent of test takers score between 420 and 750?

The question is not a GMAT type question. Moreover it looks like an incomplete question.

Recall 34:14:2 rule from our highschool maths.
420 is one SD less than Mean

750 is 2SD more than Mean

So that adds up to 34 + 34+14 = 82%

Pls explain 34:14:2 rule. I got that Highest value is 720 and lowest is 420. how these percentages are calculted.

The reason Anurag says it is an incomplete question is that it not stated the distribution of exam scores follows a normal distribution. Please take time to include all the details given in a question you are posting.

Moreover, the GMAT will not require knowledge of how to calculate the distribution of scores within a range. However, knowing how it works may be tested.

alltimeacheiver wrote:I have seen this question In Princeton Review mannual Pls advcice on same. Or let me know if it is requeired to ignore.

You definitely do not need to know about normal distributions for the GMAT.

For standard deviation, all you need to know is in general what it means and, for data sufficiency, what's required to calculate SD. You'll never have to actually calculate it on test day (so you don't need the formula).

For DS purposes, to calculate standard deviation you need:

1) the number of terms; and

2) the exact spacing of the set.

Of course, if you know all of the terms in a set, you have both (1) and (2).

The general information to remember for the GMAT:

1) SD measures how spread out the terms in the set are from the mean;

2) the higher the SD, the more spread out the set from the mean; the lower the SD, the tighter packed the set is around the mean; and

3) when comparing graphs, assuming that the scales are the same, a flatter curve means a higher standard deviation and a steeper curve means a lower standard deviation.

While the above is somewhat simplistic, it's good enough for GMAT purposes.