With reference to Exercise 67, use the formula obtained in Exercise 31 to construct a 99% confidence interval for ρ.
Exercise 67
The following data pertain to x, the amount of fertilizer (in pounds) that a farmer applies to his soil, and y, his yield of wheat (in bushels per acre):
Assuming that the data can be looked upon as a random sample from a bivariate normal population, calculate r and test its significance at the 0.01 level of significance. Also, draw a scattergram of these paired data and judge whether the assumption seems reasonable.
Exercise:
By solving the double inequality 
(with z given by the formula in the previous page) for ρ, derive a (1 - α)100% confidence interval formula for ρ.