Prices of diamonds are very sensitive to their weight (measured in carat). For example, the price of a 1 carat diamond tends to be much higher than the price of a 0.99 carats diamond. To study this phenomenon in more detail, we consider two random samples of diamonds, 0.99 carats and 1 carat, each sample of size 23. The average price of 0.99 carats diamonds in the sample is $4451, while the average price of 1 carat diamonds in the sample is $5681. From long-term studies, we know that both the prices of 0.99 carats diamonds and the prices of 1 carat diamonds are normally distributed with standard deviations ơ1 = $1332 (0.99 carats) and o2 = $1613 (1 carat), respectively. (a) Carry out a hypothesis test at significance level 0.01 to evaluate whether the true average price µi of 0.99 carats diamonds is lower than the true average price µ2 of 1 carat diamonds. Specify Ho and Ha, the test statistic, and calculate the p-value or use p-value considerations to conclude. (b) Compute the type II error probability for the test in (a) if the true average price of 1 carat diamonds is $5500 and the true average price of 0.99 carats diamonds is $4600. Include a detailed derivation in your answer. (c) How large do the sample sizes (kept equal for 0.99 carats and 1 carat diamonds) have to be such that, in the situation described in (b), the type II error probability is at most 5%? Include a detailed derivation in your answer.

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Prices of diamonds are very sensitive to their weight (measured in carat). For example, the price of
a 1 carat diamond tends to be much higher than the price of a 0.99 carats diamond. To study this
phenomenon in more detail, we consider two random samples of diamonds, 0.99 carats and 1 carat,
each sample of size 23. The average price of 0.99 carats diamonds in the sample is $4451, while the
average price of 1 carat diamonds in the sample is $5681. From long-term studies, we know that
both the prices of 0.99 carats diamonds and the prices of 1 carat diamonds are normally distributed
with standard deviations oj =
$1332 (0.99 carats) and o2 =
$1613 (1 carat), respectively.
(a) Carry out a hypothesis test at significance level 0.01 to evaluate whether the true average
price µi of 0.99 carats diamonds is lower than the true average price µ2 of 1 carat diamonds.
Specify Ho and Ha, the test statistic, and calculate the p-value or use p-value considerations
to conclude.
(b) Compute the type II error probability for the test in (a) if the true average price of 1 carat
diamonds is $5500 and the true average price of 0.99 carats diamonds is $4600. Include a
detailed derivation in your answer.
(c) How large do the sample sizes (kept equal for 0.99 carats and 1 carat diamonds) have to be
such that, in the situation described in (b), the type II error probability is at most 5%? Include
a detailed derivation in your answer.
Transcribed Image Text:Prices of diamonds are very sensitive to their weight (measured in carat). For example, the price of a 1 carat diamond tends to be much higher than the price of a 0.99 carats diamond. To study this phenomenon in more detail, we consider two random samples of diamonds, 0.99 carats and 1 carat, each sample of size 23. The average price of 0.99 carats diamonds in the sample is $4451, while the average price of 1 carat diamonds in the sample is $5681. From long-term studies, we know that both the prices of 0.99 carats diamonds and the prices of 1 carat diamonds are normally distributed with standard deviations oj = $1332 (0.99 carats) and o2 = $1613 (1 carat), respectively. (a) Carry out a hypothesis test at significance level 0.01 to evaluate whether the true average price µi of 0.99 carats diamonds is lower than the true average price µ2 of 1 carat diamonds. Specify Ho and Ha, the test statistic, and calculate the p-value or use p-value considerations to conclude. (b) Compute the type II error probability for the test in (a) if the true average price of 1 carat diamonds is $5500 and the true average price of 0.99 carats diamonds is $4600. Include a detailed derivation in your answer. (c) How large do the sample sizes (kept equal for 0.99 carats and 1 carat diamonds) have to be such that, in the situation described in (b), the type II error probability is at most 5%? Include a detailed derivation in your answer.
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