Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized for You

we will pick new questions that match your level based on your Timer History

Track Your Progress

every week, we’ll send you an estimated GMAT score based on your performance

Practice Pays

we will pick new questions that match your level based on your Timer History

Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.

It appears that you are browsing the GMAT Club forum unregistered!

Signing up is free, quick, and confidential.
Join other 350,000 members and get the full benefits of GMAT Club

Registration gives you:

Tests

Take 11 tests and quizzes from GMAT Club and leading GMAT prep companies such as Manhattan GMAT,
Knewton, and others. All are free for GMAT Club members.

Applicant Stats

View detailed applicant stats such as GPA, GMAT score, work experience, location, application
status, and more

Books/Downloads

Download thousands of study notes,
question collections, GMAT Club’s
Grammar and Math books.
All are free!

Thank you for using the timer!
We noticed you are actually not timing your practice. Click the START button first next time you use the timer.
There are many benefits to timing your practice, including:

A vending machine is designed to dispense 8 oz. of coffee [#permalink]
31 Aug 2007, 17:01

A vending machine is designed to dispense 8 oz. of coffee intto a cup. After a test that recorded the number of oz. of coffee in each of 1,000 cups dispensed by the vending machine, the 12 listed amounts, in oz., were selected from the data. If the 1,000 recorded amounts have a mean of 8.1 oz. and a standard deviation of 0.3 oz., how many of the 12 listed amounted are within 1.5 standard deviations of the mean?

Re: Gmatprep; standard deviation [#permalink]
31 Aug 2007, 17:28

gnr646 wrote:

A vending machine is designed to dispense 8 oz. of coffee intto a cup. After a test that recorded the number of oz. of coffee in each of 1,000 cups dispensed by the vending machine, the 12 listed amounts, in oz., were selected from the data. If the 1,000 recorded amounts have a mean of 8.1 oz. and a standard deviation of 0.3 oz., how many of the 12 listed amounted are within 1.5 standard deviations of the mean?

Yah, I was floored. This one came in the first GMATprep I took a couple of weeks ago. Needless to say, I completely guessed and moved on. No way was I answering that in under 2 min. Anyone have good shortcuts for stats questions like this?

Hence all values that fall under 8.1-0.45 to 8.1+0.45 is within 1.5 SD from the mean.

i.e we should look out for values between 7.65 and 8.55

There are 11 such values.

Please, can you post the formula or formulas according to which you derived text in bold...

thanks

the question states that the SD = 0.3, and asks how many of the 12 listed amounts are 1.5 within the SD, so it is SD * 1.5 = 0.3 * 1.5 = 0.45. There is no tricky formula involved. From there we find the values that would be within 0.45 from the mean/average of 8.1. This range as explained above is between 7.65 and 8.55 (+/- 0.45). Hence from the list, we see that there are 11 out of 12 amounts.

Hence all values that fall under 8.1-0.45 to 8.1+0.45 is within 1.5 SD from the mean.

i.e we should look out for values between 7.65 and 8.55

There are 11 such values.

Please, can you post the formula or formulas according to which you derived text in bold...

thanks

the question states that the SD = 0.3, and asks how many of the 12 listed amounts are 1.5 within the SD, so it is SD * 1.5 = 0.3 * 1.5 = 0.45. There is no tricky formula involved. From there we find the values that would be within 0.45 from the mean/average of 8.1. This range as explained above is between 7.65 and 8.55 (+/- 0.45). Hence from the list, we see that there are 11 out of 12 amounts.

got it,

actually, it is wording and redundant numbers that make it look complex...

1.5S.D = +/- 0.45 from mean -> so we need values between 7.65 and 8.55. There are 11 such values.

Even if you missed it, you can work out a range and pick from the choices given. 1 S.D is about 64.8% of the number of values, which works out to ~8 values are within 1 S.D. 2S.D is about 95.4% of the number of values which works out to ~slight above 11 of the values are within 2S.D. So you should be picking an answer between 8-11. Tough luck if your choices are 8,9,10,11 though....

Re: Gmatprep; standard deviation [#permalink]
02 Sep 2007, 22:20

gnr646 wrote:

A vending machine is designed to dispense 8 oz. of coffee intto a cup. After a test that recorded the number of oz. of coffee in each of 1,000 cups dispensed by the vending machine, the 12 listed amounts, in oz., were selected from the data. If the 1,000 recorded amounts have a mean of 8.1 oz. and a standard deviation of 0.3 oz., how many of the 12 listed amounted are within 1.5 standard deviations of the mean?

ughh this question lol. Its so easy, but b/c of time pressure on my GMATPrep, I got it wrong. Entered the wrong choice neway if u don't know SD well, its pretty easy to learn.

mean is 8.1 So just add 1.5(.03)=.45 to 8.1 and subtract .45 from 8.1. You get 7.65-8.55 So just find the numbers that fall inbetween these two numbers. Ans is 11.

gmatclubot

Re: Gmatprep; standard deviation
[#permalink]
02 Sep 2007, 22:20

Hello everyone! Researching, networking, and understanding the “feel” for a school are all part of the essential journey to a top MBA. Wouldn’t it be great... ...

Are you interested in applying to business school? If you are seeking advice about the admissions process, such as how to select your targeted schools, then send your questions...