The distribution of mean intensities of cDNA spots corresponding to genes that are not expressed can be assumed to be normal [276]. Let us assume that the mean of this distribution is 400 and the standard deviation is 150. We are using an array that has each gene spotted in triplicates. We calculate the expression value of a gene as the mean of its replicates.
(a) What is the probability that a spot corresponding to an unexpressed gene has a value higher than 700?
(b) What is the probability that an unexpressed gene has an expression value of 700 or higher?