<Tr> <Td> 46 </Td> <Td> Indianapolis International Airport </Td> <Td> IND </Td> <Td> Indianapolis </Td> <Td> IN </Td> <Td> 4,376,432 </Td> <Td> 4,216,766 </Td> <Td> 3,889,567 </Td> <Td> 3,605,908 </Td> </Tr> <Tr> <Td> 47 </Td> <Td> Cleveland Hopkins International Airport </Td> <Td> CLE </Td> <Td> Cleveland </Td> <Td> OH </Td> <Td> 4,562,740 </Td> <Td> 4,205,739 </Td> <Td> 4,083,476 </Td> <Td> 3,686,315 </Td> </Tr> <Tr> <Td> 48 </Td> <Td> Pittsburgh International Airport </Td> <Td> PIT </Td> <Td> Pittsburgh </Td> <Td> PA </Td> <Td> </Td> <Td> 3,986,114 </Td> <Td> 3,890,677 </Td> <Td> 3,827,860 </Td> </Tr> <Tr> <Td> 49 </Td> <Td> John Glenn Columbus International Airport </Td> <Td> CMH </Td> <Td> Columbus </Td> <Td> OH </Td> <Td> 3,765,007 </Td> <Td> 3,567,864 </Td> <Td> 3,312,496 </Td> <Td> 3,115,501 </Td> </Tr>

What percent of the world's airports are in the united states