A grocery store scanner's ability to detect a product is measured as maximum attenuation or db. The scanner was tested with 20 different...

1. A grocery store scanner's ability to detect a product is measured as "maximum attenuation" or db. The scanner was tested with 20 different products, resulting in a mean of 10.7 db and 2.4 db.

a) Is there strong evidence that the population mean maximum attenuation for all possible products is greater than 9.25db? Use a =0.01

b) Calculate a 98% confidence interval for the mean maximum attenuation.