A male factory worker smokes 30 cigarettes per day and has done so for the last 20 years. His cumulative smoking exposure, expressed in pack-years, is:

• A 10 pack-years
• B 20 pack-years
• C 30 pack-years ✓
• D 60 pack-years

Explanation

One pack-year equals 20 cigarettes smoked daily for one year. Pack-years are calculated as (number of cigarettes per day divided by 20) multiplied by years of smoking. Here, 30 divided by 20 gives 1.5 packs per day, and 1.5 multiplied by 20 years gives 30 pack-years. Choosing 60 reflects forgetting to divide by 20, a frequent calculation error in exams.

Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.

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