For problems 9 & 10 circle the best answer 9. In interval estimation, the t dist

Question

For problems 9 & 10 circle the best answer 9. In interval estimation, the t distribution is applicable only when a. the population has a mean of less than 30 b. the sample standard deviation () is given instead of the population standard deviation (o, c. the variance of the population is known. d. the standard deviation of the population is known. e. we will always use the t distribution. 10. To assess the precision of a laboratory scale, we measure a block known to have a mass of 1 gram. We measure the block n times and record the mean of the measurements. Suppose the scale readings are normally distributed with unknown mean and standard deviation 0.001 g How large should n be so that a 95% confidence interval for has a margin of error of ± 0.0001? a. 20 b. 385 c. 10,000 d. 66,358 e. 384

Explanation / Answer

Solution(9)

Its answer is B. t distribution used when the sample standard deviation is given and we estimate population standard deviation so its answer is B.

Solution(10)

Margin of error = 0.0001

SD = 0.001

N=?

Z for alpha = 0.025

Z = 1.96

Margin of error = Z*SD/sqrt(n)

0.0001= 1.96*0.001/sqrt(n)

sqrt(n) = 1.96*0.001/0.0001

Sqrt(n) = 1.96*10

sqrt(n) = 19.6

n = 19.6*19.6

n= 384.16 or 385

So its answer is b. i.e 385

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