1 . The Bright Company has developed a new charging light. They claim that the new light is function 30 minutes longer without charging compared to the old light. 35 samples of each new and old light can be used continuously for an average 600 minutes and 480 minutes, respectively with standard deviation of 20 minutes and 40 minutes. Assume that both population variances are unequal.

i) Can we accept the company's claim at 5% level of significance?[7 Marks]

ii) Based on your answer in (i), can we say that the mean life of the new light longer than the old light exactly 30 minutes without charging? Give a reason.[2 Marks]

2 . A manager claims that the average sales for her shop is RM 1800 per day during school holiday. The sample mean of the sales for first 10 days and last 10 days is RM 1880 and RM 1790, respectively with standard deviation of RM 14 and RM 13. Assume that both population variances are equal.

i) Find a 90% confidence interval of the difference mean sales between the first and last 10 days of the school holiday period. Interpret the value.

[7 Marks]

ii) If the level of confidence changed to 95%, which percentage of confidence level has a greater range? Explain why. [3 Marks]