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March 1, 2015

Posted by **Tracy** on Wednesday, June 26, 2013 at 5:07pm.

Sample Number Mean Std. Dev.

1 27 39 21

2 16 26 35

Lower Limit

Upper Limit

- math -
**Eli**, Wednesday, June 26, 2013 at 8:39pmxbar1 - 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 9:30pmThose was not the right answers, the ones that I had got previous was also close to them.

- math -
**Eli**, Wednesday, June 26, 2013 at 10:05pmFor pooled

sp = (n1-1)s1^2 + (n2-1)s2^2 /(n1+n2-2)

Sqrt(29841/41 )

= 26.978

Confidence interval

The degrees of freedom of t is n1+ n2 -2

xbar1-xbar2 -+ta/2 *sp*sqrt(1/n1 +1/n2))

(39-26)-+ 2.02* 26.978sqrt(1/27+ 1/16))

(-4.19, 30.19)

- math -
**Tracy**, Wednesday, June 26, 2013 at 11:00pmThanks, but those are wrong also.

- math -
**Kuai**, Thursday, June 27, 2013 at 4:12pmconservative degrees of freedom, you use small number. Df = 15

(39-26)-+ 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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