8-5 p411 n22
Original claim: the mean weight loss is less than zero (diet is effective)
μ < 0

The Null Hypothesis
H₀: μ = 0

The Alternate Hypothesis
H₁: μ < 0

A sample of n = 40 has 39 degrees of freedom.
For a left tailed test and a level of significance, α = 0.01
t_critical = -2.426

Data:
x_= -6.6 and s = 10.8
t_test = (-6.6-0) ⁄ (10.8 ⁄ √40) = -3.865

Because -3.865 is IN the Critical Region, we Reject the Null Hypothesis and the statistical analysis of the data can support the original claim.

Conclusion:
The sample data SUPPORT the claim that the mean weight loss is less than zero (diet is effective)