Mrs. Green, manager of a large company, frequently held meetings with other business people in a room within her building. She did not smoke, but many attendees did, leaving the air in the meeting room often unbearable.
One day, after a particularly long meeting, her throat and eyes were sore, and she was coughing persistently. To solve the problem, she called a major air conditioning company and asked them to calculate the cost of keeping the meeting room air truly clean.
A few days later, the company sent Mrs. Green two estimates to choose from. One estimate was for $5,000 to install a new air conditioning system. The other was for $5.00 to purchase a sign that read: NO SMOKING.