Consider the following summary data on the modulus of elasticity ( 106 psi) for lumber of three different grades [in close agreement with values in the article “Bending Strength and Stiffness of Second-Growth Douglas-Fir Dimension Lumber” (Forest Products J., 1991: 35–43), except that the sample sizes there were larger]:

Use this data and a significance level of .01 to test the null hypothesis of no difference in mean modulus of elasticity for the three grades.