The amount of Jen’s monthly phone bill is normally distributed with a mean of $55 and a standard deviation of $12. What percentage of her phone bills are between $19 and $91?

And we can find this probability with this difference and using the normal standard distribution

Step-by-step explanation:

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

Where and

We are interested on this probability

And we can use the z score formula given by:

Replacing the info we got:

And we can find this probability with this difference and using the normal standard distribution

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