math
posted by Tracy .
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
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
Those was not the right answers, the ones that I had got previous was also close to them.

math 
Eli
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
Thanks, but those are wrong also.

math 
Kuai
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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