How many more people, in terms of percentage, were in the two biggest age groups combined compared to the two smallest combined?
return age groups ;return percentages of #1 ;return the  two  highest of #2 ;return the  two  lowest of #2 ;return sum of #3 ;return sum of #4 ;return the  difference of #5 and  #6
['select', 'project', 'aggregate', 'aggregate', 'aggregate', 'aggregate', 'arithmetic']