Question

In a recent year, grade 8 Washington State public school students taking a mathematics assessment test had a mean score of 281 with a standard deviation of 34.4. Possible test scores could range from 0 to 500. Assume that the scores are normally distributed.

A random sample of 60 students is drawn from this population. What is the probability that the mean test score is greater than 290? Leave answers in decimal form, not percentages. Round to the nearest Hundredth (two decimal places).

Answer 1

The probability that the mean test score is greater than 290

P(X⁻ > 290 ) = 0.0217

Explanation:

Step(i):-

Mean of the Population (μ) = 281

Standard deviation of the Population = 34.4

Let 'X' be a random variable in Normal distribution

Given X = 290

`Z = (x -mean)/((S.D)/(√(n) ) ) = (290-281)/(4.44) = 2.027`

Step(ii):-

The probability that the mean test score is greater than 290

P(X⁻ > 290 ) = P( Z > 2.027)

= 0.5 - A ( 2.027)

= 0.5 - 0.4783

= 0.0217

The probability that the mean test score is greater than 290

P(X⁻ > 290 ) = 0.0217