Posted by Tracy on Wednesday, June 26, 2013 at 5:07pm.
Find the 95% confidence interval for the difference between two means based on this information about two samples. Assume independent samples from normal populations. (Use conservative degrees of freedom.) (Give your answers correct to two decimal places.)
Sample Number Mean Std. Dev.
1 27 39 21
2 16 26 35
Lower Limit
Upper Limit

math  Eli, Wednesday, June 26, 2013 at 8:39pm
xbar1  xbar2 + ta/2 * sqrt(s1^2/n2 + s2^2/n2)
13 + 2.02* sqrt(21^2/27 + 35^2 /16))
(6.47, 32.47)

math  Tracy, Wednesday, June 26, 2013 at 9:30pm
Those was not the right answers, the ones that I had got previous was also close to them.

math  Eli, Wednesday, June 26, 2013 at 10:05pm
For pooled
sp = (n11)s1^2 + (n21)s2^2 /(n1+n22)
Sqrt(29841/41 )
= 26.978
Confidence interval
The degrees of freedom of t is n1+ n2 2
xbar1xbar2 +ta/2 *sp*sqrt(1/n1 +1/n2))
(3926)+ 2.02* 26.978sqrt(1/27+ 1/16))
(4.19, 30.19)

math  Tracy, Wednesday, June 26, 2013 at 11:00pm
Thanks, but those are wrong also.

math  Kuai, Thursday, June 27, 2013 at 4:12pm
conservative degrees of freedom, you use small number. Df = 15
(3926)+ 2.13* sqrt(21^2/27 + 35^2/16))
13 + 2.13*sqrt(4459/48)
13 + 20.53
(7.53, 33.53)
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