The Professor's Response

I need help with question 18 from section 9.4. Could you please show how you get the test stat of 11.44, I get something different.
Thank You.

  See the professor's answer below.

Professor McGukian

Hi Peggy,

I can create a video for this later, but for now, let me just explain here:

Because we assume equal variances for this problem, we first need to calculate Sp²

Sp² = [(n1-1)*S1² + (n2-1)*S2²]/(n1 + n2 - 2)

(27*4.51² + 28*3.98²)/(28+29-2) = 18.04934364 = Sp²

Then our test stat formula for this problem would be:

t = (Xbar1 - Xbar2) / SqrRoot(Sp²/n1 + Sp²/n2) = (38.28 - 25.4) / SqrRoot(18.04934/28 + 18.04934/29) = 11.443

Note: the denominator part of the test stat (the part under the squareroot) should be 1.125615643. Use that to check your calculation.

Hope that helps,



Professor McGukian

Hi Peggy,

Here is a video explanation of how to work out the test statistic:



  Back to Ask the Professor