8-5 p411 n22
Original claim: the mean weight loss is zero (diet is NOT 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 two tailed test and a level of significance, α = 0.01
t_critical = -2.708 and 2.708

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 reject the original claim.

Conclusion:
There is sufficient evidence to warrant rejection of the claim that the mean weight loss is zero (diet is NOT effective)

If we REJECT the claim that the diet is NOT effective, then the diet IS effective