Answer to Question #25640 in Statistics and Probability for David
Ninety percent of all students at private universities pay less than what amount? (Round z value to 2 decimal places and your final answer to the nearest whole number.)
m = 20,132
sigma = 4,450
And we know:
P ( x < mean + z*sigma ) = 0.9
or& percentage of values expected to lie in and outside the symmetric interval& mean +- z*sigma = 80 %
From the tables: z = 1.281552 = 1.28
z*sigma = 1.28*4450 = 5696
Therefore, 90% of all students at private universities pay less than :
Answer: z=1.28,& Amount& $25828
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Using the table of the standard normal CDF the P(t<1.28) is approximately equal to 0.9, where t follows the standard normal distribution. More exact value can be found by =NORM.S.INV(0,9) in Excel, namely 1.281552, rounding to 2 decimal places gives 1.28.
But how can you find z value = 1.28?