Map Sapling Learning macmillan learning When choosing the sample size needed for
ID: 3303302 • Letter: M
Question
Map Sapling Learning macmillan learning When choosing the sample size needed for an experiment to reduce the sampling variance for a single analysis to a desired level, the sampling constant, Ks, can be used. The formula is where m is the sample mass and R is the relative standard deviation A certain analysis method was determined to have a sampling constant of Ks is required for a sampling standard deviation of ±3.0%? 31 g. What mass of sample Number How many samples of this size must be analyzed in order to give 90% confidence that the mean is known to within 2.0%? Number Enter your answer samplesas a whole number.Explanation / Answer
a) Given R = 3.5 (RSD is expressed as a percentage) and KS = 25 g, plug in values and get
mR2 = KS
====> m*(3.5)2 = (25 g)
====> m = (25 g)/(3.5)2 = 2.0408 g 2.041 g.
Therefore, the mass of the sample required is 2.041 g (ans).
b) The margin of error is 2.2%.
Use the relation
margin of error = Z*(RSD)/n where n is the number of samples analysed.
Z* = 1.645 at 90% CL.
Plug in values
2.2 = 1.645*(3.5)/n
====> n = 2.6170
===> n = 6.8489 7
Therefore, 7 replicates measurements must be made (ans).