Sampling

ping pong

Hi,
My son is doing a Quantative Analysis exam next week and is having trouble with a sample sampling question. His lecturer did not provide the solution and the notes are difficult to follow.
This is the question:
An investigation was carried out into “ Monthly Spending on Mobile Phones by Third Level students in DIT”. Twenty five females and twenty males were randomly selected. The results were as follows:

Female Expenditure/month
25 15 30 45 10
10 35 50 15 0
20 25 40 35 15
30 20 15 5 40
25 35 55 10 15


Male Expenditure/month
15 15 30 35 10
10 35 50 15 0
20 25 20 35 15
30 20 15 5 10

1) Calculate the sample average and sample standard deviation for females.
2) Calculate the sample average and sample standard deviation for males.
3) Calculate the sample average and sample standard deviation for all 45 students
You should use the statistics mode on your calculator for (1), (2) and (3)
4) Calculate a 99% confidence interval for the “Population Average Spending/month for all students”
i.e. no gender distinction
5) Interpret your interval in (4).
6) Outline the decision rules for using ‘t’ or ‘Z’ when calculating confidence intervals.
7) What sample size would be required to achieve precision of ±€2 when estimating the average
spending for all students with 99% confidence?
8) When calculating sample size in (7) what assumption did you make about Population size, was this
a reasonable assumption to make? Explain
9) What % of all students spend ≥ €20 per month.
10) Calculate a 95% confidence interval for Population Percentage who spend ≥€20 per month.
11)Interpret your interval in (10)
12) Why is the Sampling Error (precision) so large in (10)?
13) What sample size would be required to achieve precision of ± 3% when estimating the Population Percentage with 95% confidence if the total population size is 15000.
If you could give any help on this it really would be appreciated.