The tensile strength of a certain brand of polythene sheet can be modeled by a normal distribution with mean 36psi and standard deviation 4psi. ( 1) Determine the probability that the tensile strength...

The tensile strength of a certain brand of polythene sheet can be modeled by a normal distribution with mean 36psi and standard deviation 4psi. (

1) Determine the probability that the tensile strength of a sample is at least 28 psi.

(2) If the specifications require the tensile strength to exceed 30 psi, what proportion of the production has to be scrapped?