Have questions about your preparation or an upcoming test? Need help modifying the Study Plan to meet your unique needs? No problem. Just book a Skype meeting with Brent to discuss these and any other questions you may have.

- Video Course
- Video Course Overview - READ FIRST
- General GMAT Strategies - 7 videos (all free)
- Data Sufficiency - 16 videos (all free)
- Arithmetic - 38 videos (some free)
- Powers and Roots - 36 videos (some free)
- Algebra and Equation Solving - 73 videos (some free)
- Word Problems - 48 videos (some free)
- Geometry - 42 videos (some free)
- Integer Properties - 38 videos (some free)
- Statistics - 20 videos (some free)
- Counting - 27 videos (some free)
- Probability - 23 videos (some free)
- Analytical Writing Assessment - 5 videos (all free)
- Reading Comprehension - 10 videos (all free)
- Critical Reasoning - 38 videos (some free)
- Sentence Correction - 70 videos (some free)
- Integrated Reasoning - 17 videos (some free)

- Study Guide
- Your Instructor
- Office Hours
- Extras
- Prices

## Comment on

Units of Standard Deviation## Hi. I have solved this and

Why you took the numbers which are less than 6.9? Shouldn't we take more than?

Please anyone explain.

## The questions asks us to find

The questions asks us to find the values that are more than 0.5 units of standard deviation BELOW the mean.

## Why not the range of numbers

## Here's an analogous question:

Here's an analogous question: "Which of the following temperatures are more than 10 degrees below -3 degrees?"

{-24, -20, -17, -14, -8, -3, 0, 5, 11, 19}

Well, 10 degrees below -3 degrees is -13. We want temperatures that are MORE THAN 10 degrees below -3. So, these are: -24, -20, -17, and -14

Does that help?

## Hi,

What would be the ans. if the Q says "How many nos. LESS than 0.5 units from Sd/- below the mean"? Would it cover only values from 4.8 to 9 (mean) or 4.8 to 18?

Thanks

## Sorry, I'm not sure what you

Sorry, I'm not sure what you mean by "... Sd/- below the mean"

Can you please elaborate?

## Thanks for the Reply!

I just meant what would be the answer if the same question above would ask "..., how many numbers in set A are LESS than 0.5 units of standard deviation below the mean?"

## In that case, we would want

In that case, we would want all of the values that are BETWEEN 0 units of SD and 0.5 units of SD BELOW the mean.

0 units of SD BELOW the mean = 9 - 0(4.2)

= 9 - 0

= 9

O.5 units of SD BELOW the mean = 9 - 0.5(4.2)

= 9 - 2.1

= 6.9

So, the values that meet your condition are BETWEEN 6.9 and 9

So, the 7's and 8's meet this condition.

Cheers,

Brent

## Ok Thanks,

Now if you refer to the 2019, GMAT Official Q. No. 166, there they have taken all the values below

"m(mean) + d(SD)" instead of only values between "m" and "m+d".

Where is my understanding lacking?

## I have a feeling you may be

I have a feeling you may be misreading "LESS THAN 1 SD" as "BELOW THE MEAN"

You might want to review this video: https://www.gmatprepnow.com/module/gmat-statistics/video/809

Here's question #166 from the OG2019: https://gmatclub.com/forum/a-certain-characteristic-in-a-large-populatio...

The question asks "What percent of the distribution is LESS THAN m+d?"

m+d represents one unit of standard deviation above the mean.

So, for example, if the mean (m) = 10 and the SD (d) = 3, then they want all values less than 13

CONVERSELY, if the question asked "What percent of the distribution is LESS THAN 1 unit of standard deviation from the mean?", then we'd need to include all values BETWEEN m-d and m+d.

Does that help?

Cheers,

Brent

## Absolutely crystal clear,

## Add a comment