Final answer:
The 'pack year history' for smoking 2 packs per day for 20 years is 40 pack years.
Step-by-step explanation:
A 'pack year history' is a measurement used in healthcare to quantify a person's cigarette smoking history. It is calculated by multiplying the number of packs of cigarettes smoked per day by the number of years a person has smoked. In this case, the student has given a value of 2 packs per day (2ppd) for 20 years.
To calculate the 'pack year history', you simply multiply the number of packs per day (2ppd) by the number of years smoked (20 years). So, the calculation would be: 2ppd x 20 years = 40 pack years.
Therefore, the 'pack year history' for smoking 2 packs per day for 20 years would be 40 pack years.