Computing the pooled standard deviation. An experiment was run to compare three timed-release fertilizers in terms of plant growth. The sample sizes were 25, 18, and 28, and the corresponding estimated (a) Is it reasonable to use the assumption of equal standard deviations n we analyze these d (b) Give the values of the variances for the three groups. (c) Find the pooled variance. (d) What is the value of the pooled standard deviation?