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comment 7.7 standard deviations away from the mean?
Thanks so much! :)
Mar
26
comment 7.7 standard deviations away from the mean?
Thanks! I think I got it! :)
Mar
4
comment 7.7 standard deviations away from the mean?
Ah, you are correct. I'm used to automatically talking about being below the Z-value because the z-tables we use in class give the probability to the left of the z-values. So, in better words: the P(z>7.7) is approximately zero and P(z<7.7) is almost 100%?
Mar
4
comment 7.7 standard deviations away from the mean?
I see! So when you were helping me last night on my commute times problem (this 7.7 z value is from the same problem), it applies like this: a sample mean at or close to a 42-minute commute time (which gave me 7.7) is basically not going to occur (makes sense because the population mean is about 23, so 42 is waaaay up there), so the probability of the sample mean being below 42 minutes is approximately 1 (or there's nearly a 100% probability). Woo hoo! Lightbulbs are clicking!
Mar
4
comment 7.7 standard deviations away from the mean?
0.9998 is the highest probability on the z table, at z=3.49. So you're implying that, because 7.7 is so many standard deviations from the mean, that the probability is zero. Sweet!
Mar
4
comment 7.7 standard deviations away from the mean?
I see, so the chance is practically zero. I guess I've just been so bent on having a value that I was really confusing myself. Once again, thanks a ton Andre' for your help! Math is definitely not a strong subject for me :)
Mar
4
comment Find a Probability of a Normally Distributed Random Sample
Thanks! You've helped me a bunch!
Mar
4
asked 7.7 standard deviations away from the mean?
Mar
4
comment Find a Probability of a Normally Distributed Random Sample
If it's not too much to ask, I'd like one last piece of advice. I've done several more problems like this now, and they've all been correct. But a new problem (same N=2500, population mean, and population standard deviation) is asking, in a random sample of 15, what's the probability that the sample mean commute time will be between 18 and 42 minutes? I've done calculations (new standard dev=2.436928) to the point of getting z values: lower z=-2.13 and upper z=7.7. Surely I must've done something wrong, because my class only has a z table going up to a z value of 3.4! What's with the 7.7?
Mar
4
comment Find a Probability of a Normally Distributed Random Sample
Thank you so much! So the fact that N=2500 and n=10, with N>>n, means I can assume the population mean is the same (well, approximate) for the sample mean. Thanks again!
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asked Find a Probability of a Normally Distributed Random Sample
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