One alternative to using Table A-9 involves an approximation of critical values for rs given as

Here t is the t score from Table A-3 corresponding to the significance level and n - 2 degrees of freedom. Apply this approximation to find critical values of rs for the following cases.
a. n = 8, α = 0.05
b. n = 15, α = 0.05
c. n = 30, α = 0.05
d. n = 30, α = 0.01
e. n = 8, α = 0.01

12 + n - 2