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The heights of people h metres in a community are normally distributed with mean µ and standard deviation σ. It is given that P(h < 1.2) = 0.15 and P(h > 1.6) = 0.10. Calculate the mean µ and standard deviation σ of the heights of the people.
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4 partsStep-by-step solution
6 stepsHere's how to solve the problem:
Part a· 2 steps
Calculate the mean and standard deviation of the heights.
Convert the given probabilities to standard normal z-scores.
Given . We standardize this to .
From the standard normal distribution table (or calculator), the z-score corresponding to a cumulative probability of 0.15 is .
So, we have the equation:Given . This means . We standardize this to .
From the standard normal distribution table, the z-score corresponding to a cumulative probability of 0.90 is .
So, we have the equation:Solve the system of linear equations for and .
From (1):
From (2):
Subtract equation (1) from equation (2):Substitute the value of back into the first equation:
Rounding to three decimal places:
The mean is
The standard deviation is
Part b
Calculate the lower and upper quartiles.
Find the z-scores for the lower and upper quartiles.
The lower quartile () corresponds to . The z-score for 0.25 is .
The upper quartile () corresponds to . The z-score for 0.75 is .Calculate and using and .
Rounding to three decimal places:
The lower quartile is
The upper quartile is
Part c
Calculate the inter-quartile range.
The inter-quartile range (IQR) is the difference between the upper and lower quartiles.
Rounding to three decimal places:
The inter-quartile range is
Part d
Calculate .
Rewrite the inequality and standardize.
The inequality means .
Divide by :Using :
Calculate the probability.
Since the normal distribution is symmetric, .
From the standard normal distribution table, .
Rounding to three decimal places:
is
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