The amount of Jen's monthly phone bill is normally distributed with a mean of $59 and a standard deviation of $10. What percentage of her phone bills are between $29 and $89?

And we can find this probability with this difference:

And in order to find these probabilities using the normal standard distribution or excel and we got.  

So we expect about 99.735% of values between $29 and $89

Step-by-step explanation:

Let X the random variable that represent the amount of Jens 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 first in order to find a %

The z score is given by:

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

And we can find this probability with this difference:

And in order to find these probabilities using the normal standard distribution or excel and we got.  

So we expect about 99.735% of values between $29 and $89