Hi  

 t-value for a 90% confidence interval when the sample size is 20

t-value where .95 of Distribution Curve is the left of that t-value

Can use Ti:  

t = invT(.95, 19)  Check with a table or statttek.com

	CI 90%	CI 95%	CI 99%	

DF	t-value			

	0.1	0.05	0.01	0.001

1	6.31	12.71	63.66	636.62

2	2.92	4.3	9.93	31.6

3	2.35	3.18	5.84	12.92

4	2.13	2.78	4.6	8.61

5	2.02	2.57	4.03	6.87

6	1.94	2.45	3.71	5.96

7	1.89	2.37	3.5	5.41

8	1.86	2.31	3.36	5.04

9	1.83	2.26	3.25	4.78

10	1.81	2.23	3.17	4.59

11	1.8	2.2	3.11	4.44

12	1.78	2.18	3.06	4.32

13	1.77	2.16	3.01	4.22

14	1.76	2.14	2.98	4.14

15	1.75	2.13	2.95	4.07

16	1.75	2.12	2.92	4.02

17	1.74	2.11	2.9	3.97

18	1.73	2.1	2.88	3.92

19		2.09	2.86	3.88

20	1.72	2.09	2.85	3.85



Note: z-value

 = CI	z = value

90%	z =1.645

92%	z = 1.751

95%	z = 1.96

98%	z = 2.326

99%	z = 2.576



 

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