Analysis of several plant-food preparations for potassium ion yielded the following data:

The preparations were randomly drawn from the same population.
(a) Find the mean and standard deviation s for each sample.
(b) Obtain the pooled value s_pooled.
(c) Why is s_pooled a better estimate of σ than the standard deviation from any one sample?

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Sample Percent K+ 6.02, 6.04, 5.88, 6.06, 5.82 7.48, 7.47, 7.29 3.90, 3.96, 4.16, 3.96 4.48, 4.65, 4.68, 4.42 5.29, 5.13, 5.14, 5.28, 5.20 1 N345