so if we double 16 we get 32% and we have 640 residents then we ad 8% which gets us to an even number of 40% and therefor we add half the 16% to our 640 to get 800 and this is sounding complicated but stick with me. now that we have 40% of the population is 800 people then 80% is 1,600 then we add half or 20% and get 100% is 2,000 people