Respuesta :
Answer:
0.9726 = 97.26% approximate probability that X is at most 30
Step-by-step explanation:
Binomial probability distribution
Probability of exactly x sucesses on n repeated trials, with p probability.
Can be approximated to a normal distribution, using the expected value and the standard deviation.
The expected value of the binomial distribution is:
[tex]E(X) = np[/tex]
The standard deviation of the binomial distribution is:
[tex]\sqrt{V(X)} = \sqrt{np(1-p)}[/tex]
Normal probability distribution
Problems of normally distributed distributions can be solved using the z-score formula.
In a set with mean [tex]\mu[/tex] and standard deviation [tex]\sigma[/tex], the zscore of a measure X is given by:
[tex]Z = \frac{X - \mu}{\sigma}[/tex]
The Z-score measures how many standard deviations the measure is from the mean. After finding the Z-score, we look at the z-score table and find the p-value associated with this z-score. This p-value is the probability that the value of the measure is smaller than X, that is, the percentile of X. Subtracting 1 by the pvalue, we get the probability that the value of the measure is greater than X.
When we are approximating a binomial distribution to a normal one, we have that [tex]\mu = E(X)[/tex], [tex]\sigma = \sqrt{V(X)}[/tex].
11% of all steel shafts produced by a certain process are nonconforming but can be reworked (rather than having to be scrapped).
This means that [tex]p = 0.11[/tex]
Random sample of 200 shafts
This means that [tex]n = 200[/tex]
Mean and Standard deviation:
[tex]\mu = E(x) = np = 200*0.11 = 22[/tex]
[tex]\sigma = \sqrt{V(X)} = \sqrt{np(1-p)} = \sqrt{200*0.11*0.89} = 4.42[/tex]
(a) What is the (approximate) probability that X is at most 30
Using continuity correction, this is [tex]P(X \leq 30 + 0.5) = P(X \leq 30.5)[/tex], which is the pvalue of Z when X = 30.5. So
[tex]Z = \frac{X - \mu}{\sigma}[/tex]
[tex]Z = \frac{30.5 - 22}{4.42}[/tex]
[tex]Z = 1.92[/tex]
[tex]Z = 1.92[/tex] has a pvalue of 0.9726.
0.9726 = 97.26% approximate probability that X is at most 30
