Step 1 :1. Identify sample means, sample standard deviations, and sample sizes: \(\bar{x}_{night} = 2.31, s_{night} = 0.650, n_{night} = 40 \); \(\bar{x}_{day} = 2.63, s_{day} = 0.740, n_{day} = 30 \)
Step 2 :2. Calculate the difference in sample means: \(\bar{x}_{diff} = \bar{x}_{night} - \bar{x}_{day} = 2.31 - 2.63 = -0.32 \)
Step 3 :3. Calculate the pooled standard error: \(SE = \sqrt{\frac{s_{night}^2}{n_{night}} + \frac{s_{day}^2}{n_{day}}}= \sqrt{\frac{0.650^2}{40} + \frac{0.740^2}{30}} = 0.173 \)
Step 4 :4. Calculate the test statistic: \(t = \frac{\bar{x}_{diff}}{SE} = \frac{-0.32}{0.173} = -1.85 \)