Simplify the following text for a Grade 12 native English-speaking person.
Original: Together the eight countries making up the G8 represent about 14 % of the world population , but they represent about 60 % of the Gross World Product as measured by gross domestic product , all eight nations being within the top 12 countries according to the CIA World Factbook .
Simplified: The 8 countries that make up the G8 represent about 14 % of the people in the world but produce over 65 % of the world 's economic output measured by gross domestic product ( GDP ) .