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Helen [10]
3 years ago
14

The comprehensive strength of concrete is normally distributed with μ = 2500 psi and σ = 50 psi. Find the probability that a ran

dom sample of n = 5 specimens will have a sample mean diameter that falls in the interval from 2499 psi to 2510 psi.
Mathematics
1 answer:
VARVARA [1.3K]3 years ago
8 0

Answer:

The probability that the diameter falls in the interval from 2499 psi to 2510 psi is 0.00798.

Step-by-step explanation:

Let's define the random variable, X = "Comprehensive strength of concrete". We have information that X is normally distributed with a mean of 2500 psi and a standard deviation of  50 psi (or a variance of 2500 psi). In other words, X \sim N(2500, 2500).

We want to know the probability of the mean of X or \bar{X} that falls in the interval [2499;2510]. From inference theory we know that :

\bar{X} \sim N(2500, \frac{2500}{5}) \Rightarrow \bar{X} \sim N(2500,500)

Now we can find the probability as follows:

P(2499 \leq \bar{X} \leq 2510) \Rightarrow P(\frac{2499 - 2500}{500} \leq \frac{\bar{X} - 2500}{500} \leq \frac{2499 - 2500}{500} ) \Rightarrow\\\Rightarrow P(-0.002 \leq \frac{\bar{X} - 2500}{500} \leq 0.02 ) \Rightarrow P(-0.002 \leq Z \leq 0.02 )

Where Z \sim N(0,1), then:

P(-0.002 \leq Z \leq 0.02 ) \approx P(0 \leq Z \leq 0.02 ) = P(Z \leq 0.02 ) - P(Z \leq 0) \\P(0 \leq Z \leq 0.02 ) = 0.50798 - 0.5 = 0.00798

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