31. The article Characterization of Bearing Strength Factors in Pegged Timber Connections (J. Struct.

Engrg., 1997: 326—332) gave the following summary data on proportional stress limits for specimens constructed using two different types of wood:

Type of Sample Sample Sample Wood Size Mean SD Red oak 14 8.48 .79 Douglas r 10 6.65 1.28 Assuming that both samples were selected from normal distributions, carry out a test of hypotheses to decide whether the true average proportional stress limit for red oak joints exceeds that for Douglas r joints by more than 1 MPa.