As we have noted in previous chapters, even a very small effect can be significant if the if the sample is large enough. For each of the following, determine how large a sample is necessary for the correlation to be significant. Assume a two-tailed test with a = .05. (Note: Because the table does not list every possible df value, you cannot determine every possible sample size. In each case, use the sample size corresponding to the appropriate df value in the table.)
a. A correlation of r = 0.40
b. A correlation of r = 0.30
c. A correlation of r = 0.20