A survey of 100 households found that the average monthly expenditure on groceries was $400 with a standard deviation of $50.Construct a 95% confidence interval for the true average monthly expenditure of all households in the city.

A company wants to test whether a new training program has improved the performance of its employees. The scores of 10 employees before and after the program are as follows: Before: 40, 50, 55, 60, 45, 70, 80, 75, 65, 60After: 60, 70, 75, 80, 65, 85, 90, 90, 80, 75 Test at a 5% significance level whether the training program has significantly improved the employees’ scores using a paired t-test.

Skip ! A teacher has recorded the marks of 10 students in a class. The marks are:72, 85, 90, 61, 55, 78, 92, 88, 67, 80.Calculate the mean of the marks.