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a) The rainfall (in Centimeters) during the month of January in Sabah

is normally distributed with a population standard deviation of 14.25 cm. In the last 10 years, the sample average of rainfall is computed as 115.50 cm.


i. Construct a 90% confidence interval of the average rainfall in Sabah.
(2 Marks)
ii. Construct a 95% confidence interval of the average rainfall in Sabah.
(2 Marks)
iii. Comment on the width of the preceding confidence intervals. Which confidence interval is wider?
(1 Marks)


b) A sample of holiday shoppers is taken randomly from a local mall. 30 shoppers were selected and asked what their average spending on gifts would be during the entire holiday season. The point estimate of the population mean was calculated as RM500 and the sample standard deviation was calculated as RM70.


i. Construct a 95% confidence interval of the population mean spending.
(2 Marks)
ii. Construct a 95% confidence interval of the population mean spending if the sample increased to 40 shoppers.
(2 Marks)
iii. Comment on the width of the interval estimates as the sample size increases? 
(1 Marks)


         TOTAL 10 MARKS

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