280 VALUES OF Var(Put = V_ p 2 20000 , 363 Cw Cc 260 Ff FOR C = $100 AND $200 240 220 180 7] 160 1 120 100 1. 8 1 12 4 20 1 0 i 40 1 50 1. 60 1 70 4. 80 i 90 100 ALIQUOT Si ZE (w) IN GRAMS Figure 4. Approximate Values of the Variance of Average Pu Concentrations as a Function of Aliquot Size for a Composite Soil Sample Collected Approxi- mately 150 ft North of GZ at NS~-201. Suppose the purpose of the study is to estimate the average Am concentration over a defined area by randomly choosing n' soil samples from the area and analyzing n aliquots randomly drawn from each soil sample. Under the assumption of a simple cost function, Cochran finds the optimum number of aliquots per field sample to be given by the equation (in our notation) 419