Stats help?

Question

For women aged 18-24, systolic bp (in mmHg) are normally distributed with a mean of 114.8 and a standard deviation of 13.1. Hypertension is commonly defined as systolic blood pressure above 140.

If a women aged 18-24 is randomly selected what is the probability her systolic blood pressure is below 120?

Answer 1

120 - 114.8 = 5.2 mmHg

5.2 / 13.1 = 0.4 standard deviations

Using the table at

http://www.itl.nist.gov/div898/handbook/eda/section3/eda3671.htm

0.4 standard deviations = 15.5% of the population that will have a systolic BP between 114.8 and 120. Add 15.5% to the 50% that will have a systolic BP below 114.8 to get the answer that

there is a 65.5% that her systolic BP is below 120 mmHg.