Question

The number of text messsages that teenagers send per month is normally

Answer 1

Answer:

$z=\frac{4415-3400}{450}=2.26$

And the explanation of this number is:"The number of text messages for Kendra it's 2.26 deviations above the mean"

Step-by-step explanation:

1) 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".  

2) Calculate the z score

Let X the random variable that represent the number of text messages per month, and for this case we know the distribution for X is given by:

$X \sim N(3400,450)$  

Where $\mu=3400$ and $\sigma=450$

And the best way to solve this problem is using the normal standard distribution and the z score given by:

$z=\frac{x-\mu}{\sigma}$

If we apply this formula to our probability we got this:

$z=\frac{4415-3400}{450}=2.26$

And the explanation of this number is:"The number of text messages for Kendra it's 2.26 deviations above the mean"