Commercial growers of ornamental shrubs often want to retard the growth of the shrubs so t...

Commercial growers of ornamental shrubs often want to retard the growth of the shrubs so that they do not become too large prior to being sold. A growth retardant, dikegulac, was evaluated on kalanchoe, an ornamental shrub. The paper “Dikegulac alters growth and flowering of kalanchoe” [HortScience (1985) 20 : 722-724] describes the results of these experiments Ten shrubs were treated with dikegulac and another ten shrubs were untreated so the effect of the dikegulac on plant growth could be determined. The heights (in cm) of the 20 plants were measured 13 weeks after the treatment date and the summary statistics are given in the following table.

a. Construct 90% confidence intervals on the average height of the treated and untreated shrubs. Interpret these intervals.

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b. Do the two confidence intervals overlap? What conclusions can you make about the effectiveness of dikegulac as a growth retardant?