Question

The amount of Jen's monthly phone bill is normally distributed with a mean of $55 and a standard deviation of $9. Within what range are 68% of her phone bills?

Answer 1

go to
http://davidmlane.com/hyperstat/z_table.html

first click on "value from an area"
enter 0.69 into "area"
enter 55 as the mean
enter 9 as the sd

click on "between" to get:

$45.86 and $64.147

Answer 2

Use the empirical rule to solve the problem.
1) The amount of Jen's monthly phone bill is normally distributed with a mean of $55 and a standard deviation of
$12.
a) Write in the cutoffs and percentages for the phone bill.
b) What percentage of her phone bills are between $19 and $91?
c) What percentage of her phone bills are less than $67?
d) What percentage of her phone bills are greater than $79?
e) What is the median?
2