"It's not rational to treat 2+2 as 5." — logical as contrasted to illogical
"I know you're upset, but please think about this in a rational manner." — based on reason as contrasted to emotion
"When I was 10-years-old, I wasn't very smart, but I was still rational." — capable of using reason as contrasted to being insane or lacking the ability to reason
"In matters of the heart, I trust my intuition more than my rational analysis." — based on a logical analysis as contrasted to intuition, instinct, custom, tarot-card reading, or some other system of decision making
The older boys agreed; but here and there among the little ones was the doubt that required more than rational assurance.
rational = logical
There are no more uses of "rational" in Lord of the Flies.