Answer:
3.113, 4.507
Explanation:
From the given values:
Mean = 3.81
Standard deviation = 1.74
Therefore
M = √(1.72/18) = 0.4
μ = M ± t(sM)
μ = 3.81 ± 1.74*0.4
μ = 3.81 ± 0.697
Recall that the mean is estimated at 90% confidence level,
Hence,
= 90% CI [3.113, 4.507]