Answer:
220 grams.
Step-by-step explanation:
To solve this question, we need to understand the normal probability distribution and the central limit theorem.
Normal probability distribution
When the distribution is normal, we use 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.
Central Limit Theorem
The Central Limit Theorem estabilishes that, for a normally distributed random variable X, with mean
and standard deviation
, the sampling distribution of the sample means with size n can be approximated to a normal distribution with mean
and standard deviation
.
For a skewed variable, the Central Limit Theorem can also be applied, as long as n is at least 30.
In this question:
![\mu = 212, \sigma = 20, n = 22, s = \frac{20}{\sqrt{22}} = 4.264](https://tex.z-dn.net/?f=%5Cmu%20%3D%20212%2C%20%5Csigma%20%3D%2020%2C%20n%20%3D%2022%2C%20s%20%3D%20%5Cfrac%7B20%7D%7B%5Csqrt%7B22%7D%7D%20%3D%204.264)
If you pick 22 fruits at random, then 3% of the time, their mean weight will be greater than how many grams?
We have to find the 100 - 3 = 97th percentile, which is X when Z has a pvalue of 0.97. So X when Z = 1.88.
![Z = \frac{X - \mu}{\sigma}](https://tex.z-dn.net/?f=Z%20%3D%20%5Cfrac%7BX%20-%20%5Cmu%7D%7B%5Csigma%7D)
By the Central Limit Theorem
![Z = \frac{X - \mu}{s}](https://tex.z-dn.net/?f=Z%20%3D%20%5Cfrac%7BX%20-%20%5Cmu%7D%7Bs%7D)
![1.88 = \frac{X - 212}{4.264}](https://tex.z-dn.net/?f=1.88%20%3D%20%5Cfrac%7BX%20-%20212%7D%7B4.264%7D)
![X - 212 = 1.88*4.264](https://tex.z-dn.net/?f=X%20-%20212%20%3D%201.88%2A4.264)
![X = 220](https://tex.z-dn.net/?f=X%20%3D%20220)
The answer is 220 grams.