The life expectancy (at birth) of all Americans in 2014 (78.8 years) is _____ percent greater than the life expectancy in 1900 (47.3 years).

Between 2000 and 2015, the number of twin births in the United States increased by 13%, to approximately 135,000. About how many twin births were there in 2000?

78.8 / 47.3 ==1.66596 - 1 x 100 ==66.596% percentage increase in life expectancy between 1900 and 2014.