In a survey, 31 people were asked how much they spent on their child's last birthday gift. The results were roughly bell-shaped with a mean of $39 and standard deviation of $9. Construct a confidence interval at a 90% confidence level. Give your answers to one decimal place.

u = (41.659, 36.341)

Step-by-step explanation:

Constructing a 90% confidence interval for mean is given by the formulae below.

u = x + Zα/2 * σ/√n This is the upper limit

u = x - Zα/2 * σ/√n This is the lower limit.

u = population mean

x = sample mean = 39

σ = population standard deviation = 9

Zα/2 = Z score for a two tailed test with an a level of significance = 1.645 ( for 90% confidence level)

Upper limit

u = 39 + 1.645 * (9/√31)

u = 39 + 1.645 * (1.616)

u = 39 + 2.6590

u = 41.659

Lower limit

u = 39 - 1.645 * (9/√31)

u = 39 - 1.645 * (1.616)

u = 39 - 2.6590

u = 36.341

the range is 19

step-by-step explanation:

the range is biggest number minus the smallest, so in this case it would be

41 - 22 = 19

1. 3.4/4

2. 0.8/7

3. 0.5 x 3

4. 0.9 x 6

5. 10.8

6. 2.35

7. 0.567

8. 9.35

9. 0.02

10. 0.06

11. 0.16

12. 0.42

13. 0.63

14. 5.6

15. 8.1

16. 9.9

17. 0.28

18. 0.48

19. 0.27

20. 0.49

21. 0.45

22. 0.72

23. 0.9

24. 0.88

25. 0.75

26. 0.16

27. 0.328

28. 0.495

29. 0.72

30. 1.068