we know that
The fundamental concepts on which economic models (decision-making) are based:
1) Incentives
2) Trade-offs
3) Opportunity cost
4) Marginal thinking
5) Trade creates value
where
Marginal thinking compare “additional” value of 1 more unit to its price when making purchase decision (not total value/cost of all units)
In this problem
Marie is thinking about the extra benefit and cost of purchasing each additional banana. This is what economists would describe as “thinking on the margin,” or marginal thinking.
therefore
the answer is
marginal thinking