Download HON 180 Using a TI calculator or Excel to solve

HON 180 Using a TI calculator to solve problems involving the normal curve
1. Percentage under a normal curve
TI Calculator:
On a TI calculator, you can calculate the percentage under a normal curve by using the
normalcdf function.
Press 2nd Distr . “Distr” is in the third row, the fourth button from the left. “Distr” stands for
“Distributions.” Then choose “normalcdf” and press Enter “normalcdf” stands for “normal
cumulative distribution function.”
Your screen will look like
normalcdf(
Now you need to fill in the arguments of the normalcdf command. The arguments are
normalcdf(left endpoint, right endpoint, mean, SD).
This command gives the area under the normal curve from the left endpoint to the right endpoint.
Often you want the area from negative infinity to a certain endpoint or the area from a certain
endpoint to positive infinity. On a TI calculator, you should enter the very large negative
number -1EE99 in place of negative infinity, and you should enter the very large number positive
1EE99 in place of positive infinity.
Examples. For US women ages 45-55, the mean total cholesterol level is 225 mg/dl with a
standard deviation of 44 mg/dl. The distribution follows the normal curve.
a. Approximately what is the percentage of the women in this age group with cholesterol
between 200 and 250 mg/dl?
TI answer: normalcdf(200, 250, 225, 44)
b. Approximately what is the percentage of the women in this age group with cholesterol
between above 300 mg/dl?
TI answer: normalcdf(300, 1E99, 225, 44)
c. Approximately what is the percentage of the women in this age group with cholesterol
below 180 mg/dl?
TI answer: normalcdf(-1E99,180, 225, 44)
2. Percentile for a normal curve
TI Calculator:
On a TI calculator, you can calculate a percentile for normal curve using the invNorm
function.
Press 2nd Distr . Then choose “invNorm” and press Enter “invNorm” stands for “inverse
cumulative density for the normal distribution ”
Your screen will look like
invNorm(
The arguments are
invNorm(percentile rank, mean, SD).
Examples. For US women ages 45-55, the mean total cholesterol level is 225 mg/dl with a
standard deviation of 44 mg/dl. The distribution follows the normal curve.
a. The lowest 30% of women in this a group have cholesterol level less than or equal to
____________.
Answer. invNorm(0.3, 225, 44)
b. The highest 25% of women in this group have cholesterol level greater than or equal to
____________.
Answer. invNorm(0.75, 225, 44)