Place your avocados into a paper bag.
Place a ripe banana in the bag with the avocado. The banana releases ethylene, which is a gas that causes fruit to ripen.
Fold up the top of the bag so that it is closed.
Place the bag in a warm, well-ventilated location. Good ventilation prevents mold.
Remove the avocados after 24 hours, and they will be significantly softer. Repeat this process if necessary.