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A manufacturer knows that their items have a lengths that are skewed right, with a mean of 10 inches, and standard deviation of 1.6 inches. If 39 items are chosen at random, what is the probability that their mean length is greater than 10.5 inches

1 Answer

5 votes

Solution :

Given :

Mean, μ = 10 inches

Standard deviation, σ = 1.6 inches

Sample size is n = 39

Therefore,


$\mu_(\overline x)=\mu = 10$


$\sigma_(\overline x)=(\sigma)/(\sqrt n ) = (1.6)/(√(39))$

= 0.25


$P (\overline X > 10.5 ) = P\left( (\overline X - \mu_(\overline x))/(\sigma_(\overline x)) > (10.5 - 10)/(0.25) \right)$

= P( Z >2)

= 1 - P(Z < 2)

= 1 - 0.97225 (from standard normal table)

= 0.0277

User Bertus Kruger
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