A plant physiologist is planning to measure the stem lengths of soybean plants after two weeks of growth using a new fertilizer. Previous experiments suggest that the standard deviation is 1.3 cm. Using this as a guess for σ, determine how many soybean plants the researcher should have if she wants the standard error to be no more than 0.2 cm. Note that for sample size calculation we always round up to the nearest whole number. So for example if when you do the calculation you find n = 20.1 you round up to 21 You do not round down to 20 just because it is closer, because you want a sample size that gives standard error to be no more than 0.2 cm.