Method 1:Use pooled-stddev fromthe three samples
(T hink of this as a RMS average of the stddev's within each of the three groups or samples).

Method 2:

Use S(X-bar), with the central limittheorem: S(X-bar) = S(Population) / Sqrt (N)[N is sample size]

S(Population) = S(X-bar) X Sqrt (N)

T herefore:

Note that method 1 uses the stddev (within each group)while method 2 uses the stddev (between groups) = S(X-bar)

MT B >Name C10'S-pooled'
MT B >Let K1 = Stdev (C2) * Stdev (C2)
MT B >Let K2 = Stdev (C3) * Stdev (C3)
MT B >Let K3 = Stdev (C4) * Stdev (C4)
MT B >Let C10 = Sqrt ((K1 + K2 + K3) / 3)
C10 should be RMS Stdev (within):
MT B >PrintC10
S-pooled
11.2276