As a researcher in the sociology of education you are interested in the effect of different teaching methods (traditional lecture, innovative discussion, or computer assisted) on final exam scores (1-100 points).So you choose a sample of 20 students taught by each of the three teaching methods (n=60) and ask them what their final scores were.From this sample you obtain the following results.

Sums of Squares (SS)dfMean Squares (MS)

SSBetween305.23

SSWithin1427.32

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Total SS1732.55

7. What is your df within?