Answer:
5.44% probability that exactly 8 of the 16 parts you selected will have weights exceeding 45g
Step-by-step explanation:
To solve this question, we need to understand the normal probability distribution and the central limit theorem.
Normal probability distribution:
Problems of normally distributed samples are solved using the z-score formula.
In a set with mean
and standard deviation
, the zscore of a measure X is given by:
![Z = \frac{X - \mu}{\sigma}](https://tex.z-dn.net/?f=Z%20%3D%20%5Cfrac%7BX%20-%20%5Cmu%7D%7B%5Csigma%7D)
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.
Binomial probability distribution:
The binomial probability is the probability of exactly x successes on n repeated trials, and X can only have two outcomes.
![P(X = x) = C_{n,x}.p^{x}.(1-p)^{n-x}](https://tex.z-dn.net/?f=P%28X%20%3D%20x%29%20%3D%20C_%7Bn%2Cx%7D.p%5E%7Bx%7D.%281-p%29%5E%7Bn-x%7D)
In which
is the number of different combinations of x objects from a set of n elements, given by the following formula.
![C_{n,x} = \frac{n!}{x!(n-x)!}](https://tex.z-dn.net/?f=C_%7Bn%2Cx%7D%20%3D%20%5Cfrac%7Bn%21%7D%7Bx%21%28n-x%29%21%7D)
And p is the probability of X happening.
Percentage of parts with weights exceeding 45g?
1 subtracted by the pvalue of Z when X = 45. So
We have ![\mu = 43, \sigma = 4](https://tex.z-dn.net/?f=%5Cmu%20%3D%2043%2C%20%5Csigma%20%3D%204)
![Z = \frac{X - \mu}{\sigma}](https://tex.z-dn.net/?f=Z%20%3D%20%5Cfrac%7BX%20-%20%5Cmu%7D%7B%5Csigma%7D)
![Z = \frac{45 - 43}{4}](https://tex.z-dn.net/?f=Z%20%3D%20%5Cfrac%7B45%20-%2043%7D%7B4%7D)
![Z = 0.5](https://tex.z-dn.net/?f=Z%20%3D%200.5)
has a pvalue of 0.6915
1 - 0.6915 = 0.3075
If you slect 16 parts at random form that batch, what is the probability that exactly 8 of the 16 parts you selected will have weights exceeding 45g?
This is P(X = 8) when n = 16, p = 0.3075. So
![P(X = x) = C_{n,x}.p^{x}.(1-p)^{n-x}](https://tex.z-dn.net/?f=P%28X%20%3D%20x%29%20%3D%20C_%7Bn%2Cx%7D.p%5E%7Bx%7D.%281-p%29%5E%7Bn-x%7D)
![P(X = 8) = C_{16,8}.(0.3075)^{8}.(0.6915)^{8} = 0.0544](https://tex.z-dn.net/?f=P%28X%20%3D%208%29%20%3D%20C_%7B16%2C8%7D.%280.3075%29%5E%7B8%7D.%280.6915%29%5E%7B8%7D%20%3D%200.0544)
5.44% probability that exactly 8 of the 16 parts you selected will have weights exceeding 45g