'. By how much must the sample size n be increased if the width of the CI (7.5) is to be halveď? If the sample size is increased by a factor of 25, what effect will this have on the width of the interval? Justify your assertions.

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so based on 5th ques you need to ans ques 7. just help me with que 7 

5. Assume that the helium porosity (in percentage) of coal sam-
ples taken from any particular seam is normally distributed
with true standard deviation .75.
a. Compute a 95% CI for the true average porosity of a cer-
tain seam if the average porosity for 20 specimens from
the seam was 4.85.
b. Compute a 98% CI for true average porosity of another
seam based on 16 specimens with a sample average poros-
ity of 4.56.
c. How large a sample size is necessary if the width of the
95% interval is to be .40?
d. What sample size is necessary to estimate true average
porosity to within .2 with 99% confidence?
7. By how much must the sample size n be increased if the
width of the CI (7.5) is to be halved? If the sample size is
increased by a factor of 25, what effect will this have on the
width of the interval? Justify your assertions.
Transcribed Image Text:5. Assume that the helium porosity (in percentage) of coal sam- ples taken from any particular seam is normally distributed with true standard deviation .75. a. Compute a 95% CI for the true average porosity of a cer- tain seam if the average porosity for 20 specimens from the seam was 4.85. b. Compute a 98% CI for true average porosity of another seam based on 16 specimens with a sample average poros- ity of 4.56. c. How large a sample size is necessary if the width of the 95% interval is to be .40? d. What sample size is necessary to estimate true average porosity to within .2 with 99% confidence? 7. By how much must the sample size n be increased if the width of the CI (7.5) is to be halved? If the sample size is increased by a factor of 25, what effect will this have on the width of the interval? Justify your assertions.
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