df = n - 1 = 52 - 1 = 51
Step 3: Find the t-value for a 90% confidence level with 51 degrees of freedom.
For a 90% confidence interval, the alpha level ($\alpha$) is 1 - 0.90 = 0.10.
Since it's a two-tailed test, we look for $t_{\alpha/2, df} = t_{0.05,
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