Principles of Microeconomics: does John show diminishing marginal utility for coke, or does he show increasing marginal utility for coke?

Principles of Microeconomics

John likes Coca-Cola. After consuming one Coke, John has a total utility of 10 utils. After two Cokes, he has a total utility of 25 utils. After three Cokes, he has a total utility of 50 utils.

  • Does John show diminishing marginal utility for Coke, or does he show increasing marginal utility for Coke?
  • Suppose that John has $3 in his pocket. If Cokes cost $1 each and John is willing to spend one of his dollars on purchasing a first can of Coke, would he spend his second dollar on a Coke, too?
  • What about the third dollar? If John’s marginal utility for Coke keeps on increasing no matter how many Cokes he drinks, would it be fair to say that he is addicted to Coke?