Wang Yingzhijie, a senior student at Nanjing Foreign Language School, has just received an offer from Yale University. Her classmate Cui Jiaming has received an offer from Wellesley College.

These two top students are good friends. They both love to apply mathematics to daily life, to the extent that they have created a new formula to calculate a person's obesity level, which they call the Integrated Obesity Index (IOI).

Wang said: "We are both interested in using math to solve practical problems. I began to have doubts about the scientific reliability of the popular Body Mass Index (BMI), so I told Cui Jiaming. She is really good at math. And we decided to research the subject."

BMI is a general tool used to measure the size of the human body. BMI = weight (in kg)/height (in m)^2. A BMI greater than 25 indicates that an individual is overweight, and BMI greater than 30 means obesity. However, if two people have the same weight and height, and one takes exercise regularly and is muscular, while the other takes no exercise at all, they will have the same BMI. In such cases this index is inaccurate in describing the obesity level.

"In fact there is another concept called body fat percentage, which is the diagnostic criterion for obesity," says Wang. "But medical equipment is required in order to measure body fat percentage, so it is not convenient for ordinary people. So we thought about introducing the waist-hip ratio (WHR) into the calculation." Based on census data concerning diabetes and metabolic syndrome from Jiangsu province, Wang and Cui spent a whole summer vacation creating a new formula to calculate a person's obesity level. 　

The Obesity index created by the two girls is:

　　IOI=BMI×［5/39×(WHR^2+WHR)+1/3］　　

The calculation is based on height, weight, waistline and hipline.

For example：

A is 1.5m and 50kg and B is 1.65m and 60kg. A has a greater BMI. But if the WHR of A is 7:9, while the WHR of B is 1:1, then according to the IOI, B has a higher obesity level.