Your roommate is studying to be a chef and likes to try new recipes. He leaves his delicious creations in the refrigerator for anyone who wants to eat them. The food he leaves is always gone within a day. This is an example of:

a positive externality

Explanation:

A positive externality is said to occur when a good or service that is produced or consumed by an individual for his benefits, also benefits another third party.

In the scenario sited in the question above about my roommate, his trying of new recipes does not only help him in his pursuit of being a good chef, but also serves as a benefit to other people who eat his delicious creations he left available in the fridge to anyone to have access to. This is an example of a positive externality.

do your own work

you really need to do your own work and stop cheating

answer; a cost benefit analysis;