A study reported in the article “Leakage of Intracellular Substances from Alfalfa Roots...

A study reported in the article “Leakage of Intracellular Substances from Alfalfa Roots at Various Subfreezing Temperatures” (Crop Science [1991]: 1575– 1578) considered a quadratic regression model to relate y =5 MDH activity (a measure of the extent to which cellular membranes suffer extensive damage from freezing) to x= 5 electrical conductivity (which describes the damage in the early stages of freezing). The estimated regression function was

a. Supposing that n = 50, does the quadratic model appear to be useful? Test the appropriate hypotheses. b. Using calculate a confidence interval with confidence level 90% for true average MDH activity when conductivity is 40.