system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do planes fly at high altitudes? Wouldn't flying higher increase the duration of the flight?
gpt
No, they actually decrease the length and fuel consumption of the flight by decreasing air resistance. At 35,000 feet, you're higher than Mount Everest, and you have something like half the air around you. Half the air means half the air resistance, which means you can go faster with less fuel.