3. A recent survey found households of Macau intended to spend an average of $649 during the Mid-Autumn Festival. Assume

[answerhappygod]

3. A recent survey found households of Macau intended to spend
an average of $649 during the Mid-Autumn Festival. Assume that the
survey included 600 households and that the sample standard
deviation was $175.
a. What is the 95% confidence interval estimate of the population
mean?
b. The prior year, the population mean expenditure per household
was $632. At 5% significance level, can we conclude that the mean
expenditure of this year has changed? Explain.
c. Suppose you want to reduce the width of the 95% confidence
interval obtained in part (a) by half. Determine the minimum sample
size needed to achieve this. Assuming that the population standard
deviation is not significantly different from $175.