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Women comprise 83.3% of all elementary school teachers. In a random sample of 300 elementary school teachers, what is the probability that fewer than 260 are women?

Sagot :

Using the normal approximation to the binomial, it is found that there is a 0.9319 = 93.19% probability that fewer than 260 are women.

In a normal distribution with mean [tex]\mu[/tex] and standard deviation [tex]\sigma[/tex], the z-score of a measure X is given by:

[tex]Z = \frac{X - \mu}{\sigma}[/tex]

  • It 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, which is the percentile of X.
  • The binomial distribution is the probability of x successes on n trials, with p probability of a success on each trial. It can be approximated to the normal distribution with [tex]\mu = np, \sigma = \sqrt{np(1-p)}[/tex].

In this problem:

  • Women comprise 83.3% of all elementary school teachers, hence [tex]p = 0.833[/tex]
  • A sample of 300 teachers is taken, hence [tex]n = 300[/tex]

The mean and the standard deviation for the approximation are given by:

[tex]\mu = np = 300(0.833) = 249.9[/tex]

[tex]\sigma = \sqrt{np(1 - p)} = \sqrt{300(0.833)(0.167)} = 6.46[/tex]

Using continuity correction, as the binomial distribution is discrete and the normal distribution is continuous, the probability that fewer than 260 are women is P(X < 260 - 0.5) = P(X < 259.5), which is the p-value of Z when X = 259.5, hence:

[tex]Z = \frac{X - \mu}{\sigma}[/tex]

[tex]Z = \frac{259.5 - 249.9}{6.46}[/tex]

[tex]Z = 1.49[/tex]

[tex]Z = 1.49[/tex] has a p-value of 0.9319.

0.9319 = 93.19% probability that fewer than 260 are women.

A similar problem is given at https://brainly.com/question/25347055

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