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Lera25 [3.4K]
3 years ago
6

The weights of the fish in a certain lake are normally distributed with a mean of 12 lb and a standard deviation of 6. If 4 fish

are randomly​ selected, what is the probability that the mean weight will be between 9.6 and 15.6 ​lb? Round your answer to four decimal places.
Mathematics
2 answers:
Norma-Jean [14]3 years ago
6 0

Answer:

The probability that the mean weight will be between 9.6 and 15.6 ​lb is 0.6731

Step-by-step explanation:

Here we have

P(9.6≤\bar{x}≤15.6)

Therefore, we have

z=\frac{\bar{x}-\mu }{\frac{\sigma }{\sqrt{n}}}

Where:

\bar{x} = Sample mean

μ = Population mean = 12

σ = Population standard deviation = 6

n = Sample size = 4

When \bar{x} = 9.6 we have

z=\frac{9.6-12 }{\frac{6 }{\sqrt{4}}} = -0.8

From Z table, that is 0.21186

When \bar{x} = 15.6 we have 1.2

z=\frac{15.6-12 }{\frac{6 }{\sqrt{4}}} = 1.2

From Z table, that is 0.88493

0.88493 - 0.21186 = 0.67307

P(9.6≤\bar{x}≤15.6) = 0.67307 which is 0.6731 to four decimal places.

DochEvi [55]3 years ago
5 0

Answer:

P(9.6 < \bar X

And using the normal standard distribution or excel we got:

P(9.6 < \bar X

Step-by-step explanation:

Previous concepts

Normal distribution, is a "probability distribution that is symmetric about the mean, showing that data near the mean are more frequent in occurrence than data far from the mean".

The Z-score is "a numerical measurement used in statistics of a value's relationship to the mean (average) of a group of values, measured in terms of standard deviations from the mean".  

Solution to the problem

Let X the random variable that represent the weights of a population, and for this case we know the distribution for X is given by:

X \sim N(12,6)  

Where \mu=12 and \sigma=6

Since the dsitribution for x is normal then we know that the distribution for the sample mean \bar X is given by:

\bar X \sim N(\mu, \frac{\sigma}{\sqrt{n}})

We want to find this probability:

P(9.6 < \bar X

And we can use the z score formula given by;

z = \frac{\bar X -\mu}{\frac{\sigma}{\sqrt{n}}}

And if we find the z score for the limits given we got:

z = \frac{9.6-12}{\frac{6}{\sqrt{4}}}= -0.8

z = \frac{15.6-12}{\frac{6}{\sqrt{4}}}= 1.2

So we can calculate this probability like this:

P(9.6 < \bar X

And using the normal standard distribution or excel we got:

P(9.6 < \bar X

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