I am attempting a self study question on confidence interval. My answer worked out to be $20.4 \pm 1.411$. However, the model answer appeared to be $20.4 \pm 1.486$. I am pretty confidence that I am correct. I'd appreciate if anyone could give me some advice and validation please?
The owner of a big egg farm wants to estimate the mean number of eggs laid per chicken. A sample of 25 chickens shows they laid an average of 20.4 eggs per month with a standard deviation of 3.6 eggs per month. Assume the number of eggs laid per chicken per month has a normal distribution. Construct a 95% confidence interval estimate for the population mean number of eggs laid per chicken per month.