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StClowers
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In order to estimate the mean amount of time computer users spend on the internet each month, how many computer users must be surveyed in order to be 95% confident that your sample mean is within 15 minutes of the population mean? Assume that the standard deviation of the population of monthly time spent on the internet is 192 min.
The minimum sample size required is ___ computer users.
What is a major obstacle to getting a good estimate of the population mean?
a. The data does not provide information on what the computer users did while on the internet.
b. There may not be 630 computer users to survey
c. It is difficult to precisely measure the amount of time spent on the internet, invalidating some data values.
d. There are no obstacles to getting a good estimate of the population mean.
 7 months ago
 7 months ago
StClowers Group Title
In order to estimate the mean amount of time computer users spend on the internet each month, how many computer users must be surveyed in order to be 95% confident that your sample mean is within 15 minutes of the population mean? Assume that the standard deviation of the population of monthly time spent on the internet is 192 min. The minimum sample size required is ___ computer users. What is a major obstacle to getting a good estimate of the population mean? a. The data does not provide information on what the computer users did while on the internet. b. There may not be 630 computer users to survey c. It is difficult to precisely measure the amount of time spent on the internet, invalidating some data values. d. There are no obstacles to getting a good estimate of the population mean.
 7 months ago
 7 months ago

This Question is Closed

mathmale Group TitleBest ResponseYou've already chosen the best response.1
This topic is closely related to confidence intervals and uses most or all of the same parameters (variables). Pls bring me up to date: What type of references do you have available? Do you have a textbook, a list of statistics formulas, skill in looking things up on the 'Net, or ... ?
 7 months ago

mathmale Group TitleBest ResponseYou've already chosen the best response.1
This web site is a bit too advanced, but does present the formula you need for minimum sample size: http://www.itl.nist.gov/div898/handbook/prc/section2/prc222.htm About 3/4 of the way from the top of the first page, there's a formula that begins with N. That's the one we need to consider here.
 7 months ago

StClowers Group TitleBest ResponseYou've already chosen the best response.1
I have a Ti84 calc.....
 7 months ago

StClowers Group TitleBest ResponseYou've already chosen the best response.1
I see several formulas that begin with N lol
 7 months ago

StClowers Group TitleBest ResponseYou've already chosen the best response.1
@mathmale ...will the formula be N\[\ge \left(\begin{matrix}15 \\ 192\end{matrix}\right)^{2}\delta ^{2}\]
 7 months ago

StClowers Group TitleBest ResponseYou've already chosen the best response.1
I dunno how to solve it though...can you tell me which number goes where
 7 months ago

mathmale Group TitleBest ResponseYou've already chosen the best response.1
Glad you're at least trying something. If y ou'll look at the formula in that web site again, you'll see several quantities: 1.96 is called the zcritical value and is connected with a 95% confidence interval; the quantity in the denominator is the tolerance (which in this problem is 15 min) and that sigma is the std. deviation. I'd like to take a lot more time to explain this in more depth, but it does appear to me that you have all the info you need to calculate N.
 7 months ago

StClowers Group TitleBest ResponseYou've already chosen the best response.1
im trying to enter it in my Ti84 and not sure how to do it...
 7 months ago

StClowers Group TitleBest ResponseYou've already chosen the best response.1
@mathmale
 7 months ago

mathmale Group TitleBest ResponseYou've already chosen the best response.1
\[(\frac{ 1.96 }{ 15 })^{2}(192)^{2}\] is waht y ou want to calculate. Are you comfortable using parentheses on your calculator?
 7 months ago

StClowers Group TitleBest ResponseYou've already chosen the best response.1
yes i think so...i will find out lol
 7 months ago

StClowers Group TitleBest ResponseYou've already chosen the best response.1
so I got 2.27 Is that right?
 7 months ago

mathmale Group TitleBest ResponseYou've already chosen the best response.1
I haven't actually done it myself, but if you wouldn't mind, I'm going to lead you thru this calculation again. Type this into your calc.: (1.96/15) (in precisely that order) and then press the 2 x key on the left side of your calculato0r keyboard. What do you get?
 7 months ago

mathmale Group TitleBest ResponseYou've already chosen the best response.1
Note that the 2 x key, when pressed, will square the quantity within parentheses for you after you've pressed the ENTER key.
 7 months ago

StClowers Group TitleBest ResponseYou've already chosen the best response.1
when i typed that in, I typed 2 then the 2x key and it put 2^2, is that right?
 7 months ago

StClowers Group TitleBest ResponseYou've already chosen the best response.1
nevermind, got it...lol i got .0170737778
 7 months ago

mathmale Group TitleBest ResponseYou've already chosen the best response.1
sorry, i didn't see what y ou'd typed and was waiting. Plese clear the calculator.
 7 months ago

mathmale Group TitleBest ResponseYou've already chosen the best response.1
Type in ( 1.96 / 15 ) x^2 and ENTER in that order. you should obtain 0.01707.
 7 months ago

StClowers Group TitleBest ResponseYou've already chosen the best response.1
did you see what i got...i think we typed at the same time....
 7 months ago

StClowers Group TitleBest ResponseYou've already chosen the best response.1
yes i got that same answer
 7 months ago

mathmale Group TitleBest ResponseYou've already chosen the best response.1
Ooops. Do you have 0.017... still displayed? if so, pls don't erase it.
 7 months ago

StClowers Group TitleBest ResponseYou've already chosen the best response.1
yes i do
 7 months ago

StClowers Group TitleBest ResponseYou've already chosen the best response.1
so then i would type (192)^2 ?
 7 months ago

mathmale Group TitleBest ResponseYou've already chosen the best response.1
Great. Now we're going to do the last part of the calculation. keeping that 0.01707 as it is, type in the following: 2 x 192 x ENTER in that order. The first x stands for multiplication and is a key by itself on the right side of your calc, and the 2 x is the same command key you used earllier.
 7 months ago

mathmale Group TitleBest ResponseYou've already chosen the best response.1
I got the result 141616.7, which I rounded up to 141617.
 7 months ago

StClowers Group TitleBest ResponseYou've already chosen the best response.1
i got 629.407 ...?!?!
 7 months ago

mathmale Group TitleBest ResponseYou've already chosen the best response.1
Let me check my own work. Actually, your result looks more reasonable than does mine!!
 7 months ago

mathmale Group TitleBest ResponseYou've already chosen the best response.1
How extremely embarrassing. You're right; I'm wrong. You must now round up (not down) to the nearest integer number N. What's your N?
 7 months ago

StClowers Group TitleBest ResponseYou've already chosen the best response.1
my N is 629.408 ? is that right? or maybe 629.41
 7 months ago

StClowers Group TitleBest ResponseYou've already chosen the best response.1
oh wait....actually that would be 629
 7 months ago

StClowers Group TitleBest ResponseYou've already chosen the best response.1
since its asking for number of computer users
 7 months ago

mathmale Group TitleBest ResponseYou've already chosen the best response.1
What I meant was that you must eliminate all decimal fractions in your result by rounding up appropriately. 629.4077 has that decimal fraction 0.4077, which we do NOT want. MUST roud up to the nearest integer. Try again.
 7 months ago

mathmale Group TitleBest ResponseYou've already chosen the best response.1
Obviously we don't want to see 0.4077 computer user. Bloody. :)
 7 months ago

mathmale Group TitleBest ResponseYou've already chosen the best response.1
You've rounded down. We MUST round UP to be conservative in our estimate.
 7 months ago

mathmale Group TitleBest ResponseYou've already chosen the best response.1
round 629.4077 UP to the nearest integer.
 7 months ago

StClowers Group TitleBest ResponseYou've already chosen the best response.1
oh yeah...sorry bout that....it would be 630?
 7 months ago

mathmale Group TitleBest ResponseYou've already chosen the best response.1
Right. Perfect. You went beyond what the question asked you for; you have enuf data to choose the fourth possible answer as the correct answer, and you went thru the actual calculations to find N=630, the number of computer users you must survey (poll) in order to be no more than 15 min off the true population mean of the total time the pop of computer users spends on the Internet/month.
 7 months ago

mathmale Group TitleBest ResponseYou've already chosen the best response.1
Very, very good. Thanks for your persistence and positive attitude.
 7 months ago

StClowers Group TitleBest ResponseYou've already chosen the best response.1
Thank you so much!!! You are the best helper on here indeed...its so true...not many take these steps and time to explain. :)
 7 months ago

mathmale Group TitleBest ResponseYou've already chosen the best response.1
While this in itself is not sufficient practice, you've made huge, positive strides towards learning this material!
 7 months ago

mathmale Group TitleBest ResponseYou've already chosen the best response.1
thank you! I've been on the Internet nearly 12 hours today, so need to log off; I urge you to post each new part of this same problem and see if someone can help you. I may be on the 'Net tomorrow (but probably not).
 7 months ago

StClowers Group TitleBest ResponseYou've already chosen the best response.1
ok thank you so much!
 7 months ago

mathmale Group TitleBest ResponseYou've already chosen the best response.1
Great pleasure! Bye.
 7 months ago
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