Chapter 2: Understanding Variables and Solving Equations 
Numbers in the Real World

Body Mass Index

BMI (Body Mass Index) compares your height and weight to determine whether you are at risk for weight-related health problems. Typically, the lower your BMI, the lower your risk for certain health problems.  The expression for the BMI is

where the weight is in pounds and the height is in inches.  The ideal BMI range for women is 18-25 and for men 20-25.  Any BMI values outside of those ranges could be telling you something.  Always remember, the BMI does not measure body composition (i.e., fat vs thin).  It just tells you the relationship between your weight and height.

For a 6'2" male weighing 250 lb., what is his BMI?  We substitute 250 in for weight and 74 in for height.


The BMI value is 32.1.  The value is outside the preferred range for men, and to reduce his BMI to 25, he would have to weigh only 195 lb.  To find this value, keep the height at 74 and reduce the weight value until an answer of 25 appears.

Compute your own BMI as well as the BMI of those you feel comfortable asking their weight and height.