Practical statistical errors on a weight basis

The experimental percentage standard deviation can be calculated from experimental data using the following equation  

Consider a binary powder with a bulk of 800 g made up of a 40 60 mixture of particles of weight 0.05 g and 0.10 g. Determine the required gross sample weight, assuming perfect sampling, for a 2% standard deviation. From equation (1.10). 

Experimental data (g) Calculated data using equations (1.10) and (1.11)  

Sampling technique Percentage standard deviation a% Estimated maximum sample error (E%) Efficiency (C%) 

Any powder can be considered as being made up of two components, the fraction above and the fraetion below a certain size. For a reduction of 16 to I during sampling with average oversize weight = 0.10 g, and 

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