In the year 2000, over 80 million metric tons of nitrogen fertilizers were used in producing food for the world’s 6 billion people. Food production, use of nitrogen fertilizers, and world population all had grown over the preceding 40 years, but at somewhat different rates. During this time, food production grew slightly faster than population while relatively little additional land was converted to agricultural use. Fertilizer use grew most rapidly. Compare the world population index for 1960 to the world population index for 2000. Then express the world population in 2000 as a percentage of world population in 1960.