4. 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):

Grade J si 1 10 1.63 .27 2 10 1.56 .24 3 10 1.42 .26 Use this data and a signi cance level of .01 to test the null hypothesis of no difference in mean modulus of elasticity for the three grades.