Question

Annie was told that her math test score was 3 standard deviations below the mean. If test scores were approximately normal with μ=99 and σ=4, what was Annie's score? Do not include units in your answer. For example, if you found that the score was 99 points, you would enter 99.

Answer 1

Answer:

$X \sim N(99,4)$  

Where $\mu=99$ and $\sigma=4$

We want to find the Annie's score takign in count that the score is 3 deviations below the mean, so then we can find the value with this formula:

$X = \mu -3\sigma$

And replacing we got:

$X = 99 -3*4 = 87$

So then the Annie's score would be 87

Step-by-step explanation:

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

$X \sim N(99,4)$  

Where $\mu=99$ and $\sigma=4$

We want to find the Annie's score takign in count that the score is 3 deviations below the mean, so then we can find the value with this formula:

$X = \mu -3\sigma$

And replacing we got:

$X = 99 -3*4 = 87$

So then the Annie's score would be 87