Page 67 - Petrology of Sedimentary Rocks

(2) A coin weighs an average of 15.0 gm as minted. Due to irregulariCes in the
minting process, the standard deviation is 0.6 gm. Ten percent of the coins will be
heavier than what weight? The table is constructed to give us the percentage of
samples falling outside the given range, both above and below; we need only the ones
higher, therefore we look in column 2 for twice IO%, or 20%; the corresponding value is
1.3 standard deviations. In other words, 20% of the samples will fall outside the range
of X + I .3a, 10% being below and IO% above. 1.3 standard deviations in this case is
about 0.8 gm; therefore the answer is 15.8 gm.

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