Question

The weight of each “Golden Dairy’s Probiotic Yogurt with Fruit” cup is normally distributed with a mean of 170 grams and a standard deviation of 12 grams. One package contains six random cups and any package with an average weight per cup lower than 158 grams will be rejected.
Part A: What fraction of packages will be rejected because the average weight is too low?
Part B: In addition to original rejection criteria, suppose any packages that have an average weight per cup higher than 179 grams must be rejected as well. What is the total fraction of packages that will be accepted?

Answer 1

Using the normal distribution, it is found that:

A. 0.0071 = 0.71% of packages will be rejected because the average weight is too low.

B. 0.96 = 96% of packages that will be accepted.

Normal Probability Distribution

The z-score of a measure X of a normally distributed variable with mean $\mu$ and standard deviation $\sigma$ is given by:

$Z = \frac{X - \mu}{\sigma}$

• The z-score measures how many standard deviations the measure is above or below the mean.

• Looking at the z-score table, the p-value associated with this z-score is found, which is the percentile of X.

• By the Central Limit Theorem, the sampling distribution of sample means of size n has standard deviation $s = \frac{\sigma}{\sqrt{n}}$.

For this problem, the parameters are given as follows:

$\mu = 170, \sigma = 12, n = 6, s = \frac{12}{\sqrt{6}} = 4.9$

Item A:

The proportion is the p-value of Z when X = 158, hence:

$Z = \frac{X - \mu}{\sigma}$

By the Central Limit Theorem

$Z = \frac{X - \mu}{s}$

$Z = \frac{158 - 170}{4.9}$

Z = -2.45

Z = -2.45 has a p-value of 0.0071.

0.0071 = 0.71% of packages will be rejected because the average weight is too low.

Item B:

The proportion that will be accepted is the p-value of Z when X = 179 subtracted by the p-value of Z when X = 158, hence:

X = 179:

$Z = \frac{X - \mu}{s}$

$Z = \frac{179 - 170}{4.9}$

Z = 1.84

Z = 1.84 has a p-value of 0.9671.

X = 158:

$Z = \frac{X - \mu}{s}$

$Z = \frac{158 - 170}{4.9}$

Z = -2.45

Z = -2.45 has a p-value of 0.0071.

0.9671 - 0.0071 = 0.96 = 96% of packages that will be accepted.

More can be learned about the normal distribution at https://brainly.com/question/4079902

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