Question 1037365
Let P stand for probability and X be the normal distribution variable
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the problem asks us to calculate
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P ( X < 25 )
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since the sample size is > 30, we use the normal distribution and apply the Central Limit Theorem 
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the sample mean is taken to be the population mean
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the sample standard deviation is taken to be population mean / square root of sample size
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sample standard deviation = 2.5 / square root(55) = 0.337099931
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the z-value is ( X - mean ) / sample standard deviation
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z-value = ( 25 - 24.7 ) / 0.337099931 = 0.889943819 approx 0.89
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now consult the table of z-values
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P ( X < 25 ) = 0.8133
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