To solve this problem, we start by denoting the total number of people at the dinner as ( N ).
South Americans: Given that 1/5 of the people were from South America, the number of South Americans is: [ \frac{1}{5}N ]
North Americans: It is stated that the number of North Americans was 2/3 greater than the number of South Americans. First, calculate 2/3 of the number of South Americans: [ \frac{2}{3} \times \frac{1}{5}N = \frac{2}{15}N ] Then, add this to the number of South Americans to find the total number of North Americans: [ \frac{1}{5}N + \frac{2}{15}N = \frac{3}{15}N + \frac{2}{15}N = \frac{5}{15}N = \frac{1}{3}N ]
Sum of South Americans and North Americans: [ \frac{1}{5}N + \frac{1}{3}N = \frac{3}{15}N + \frac{5}{15}N = \frac{8}{15}N ]
Neither South Americans nor North Americans: The fraction of people who were neither from South America nor North America is: [ 1 - \frac{8}{15} = \frac{15}{15} - \frac{8}{15} = \frac{7}{15} ]
Therefore, (\frac{7}{15}) of the people at the dinner were from neither South America nor North America.