In May 1997, Calgary-based Bre-X Minerals collapsed when its gold assets were revealed to be dramatically less than had been claimed. Did this collapse affect the prices of other mining stocks?
a. Using the price data below, construct a 98% confidence interval for the mean difference of their pre-collapse prices minus their prices three months later.
b. At the 0.01 level of significance, does the evidence support a claim that the prices of mining stocks dropped during the period?

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Stock Before the collapse 14 12 . 0.280 2.73 After the collapse 0.7 05 0.41 0.225 2.06 A B CD E