"total registration of 749,917 people out of a state of 1.4 million" is a misleading number, sorry.  You need to factor in what % of the population is 18 and over, which according to the census is 1.1 million (78.3% of 1.4):  http://files.hawaii.gov/dbedt/census/popestimate/2015_state_pop_hi/2015_popest_sumtab.pdf