# standard

• Mar 24th 2008, 06:23 AM
aawb9c
standard
I feel like such an idiot, I just do not understand this statistics stuff! I have two stumpers on this quiz I am trying to do. Any guidance would be very appreciated!!!

1) The batteries used in a digital watch have an operating life that is normally distributed. A sample of 16 batteries reveals a mean of 3.45 yrs and a standard deviation of 0.3 yrs. For 15 df, the area in the two-tailed test is 0.05 (t=2.131) and the area in the two-tailed test is 0.10 (t=1.753).

a) The upper bound of a 95% confidence interval is?
b) The upper bound of a 90% confidence interval is?
c) The lower bound of a 95% confidence interval is?

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2) Approximately 20% of the population belongs to a health maintenance organization (HMO). Assume that for a randomly selected group of 20 adults, the number belonging to an HMO has a binomial distribution.

a) The probability of finding exactly 5 in the 20 who belong to an HMO is?
b) The probability of finding at least one in the 20 who belongs to an HMO is?
c) The probability of finding at most 8 in the 20 who belong to an HMO is?
d) The probability of finding between 2 and 5 (2 and 5 are not included) in the 20 who belong to an HMO is?

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THANK YOU SOOO MUCH. If you can just give me a formula to use, I will try to solve them myself. I'm trying to learn, it's just not coming easily to me!

Ashley
• Mar 24th 2008, 06:39 AM
TheHolly
RE: I'm so lost!!!! :(
Ashley, I know that for the first problem you need to use the fact that the mean plus or minus standard deviation, mean plus or minus 2 * standard deviation, and mean plus or minus 3 * standard deviation gives you the confidence intervals. I am not really sure how the area plays into that, but maybe that will help.
• Mar 24th 2008, 06:56 AM
aawb9c
Thx!
I appreciate your feedback. That helps a little bit. I just wish I knew what the formula was so I could plug in the numbers I have and get an answer! It drives me crazy when I can't figure something out.