Final answer:
Ellie should consider 1) the Cost-Benefit Principle when deciding between Econ 201 or Bus 101, taking into account the opportunity costs and marginal benefits to make the most informed decision.
Step-by-step explanation:
Ellie is trying to make a decision between taking Econ 201 or Bus 101 at 10:20 next quarter. To make an informed decision, Ellie would be best guided by the Economic Principle that incorporates elements of both cost-benefit analysis and opportunity cost. Specifically, she should consider the Cost-Benefit Principle, which will allow her to weigh the potential benefits of each class against the potential costs (including opportunity costs), and thus decide which course offers the greater net benefit.
The Concept of Opportunity Cost is particularly relevant here, as it refers to what someone must give up to obtain what they desire. In other words, Ellie needs to evaluate what she would be foregoing by not taking the other class. It's essential that Ellie evaluates both the direct costs and the opportunity costs of taking one class over the other, which includes considering how either class would benefit her future career and academic goals.
Additionally, it might be beneficial for her to apply The Marginal Principle, where she assesses the additional benefit of one more unit (in this case, one course) against its additional cost. For optimal decision-making, she must ensure that the marginal utility of the class she chooses exceeds the opportunity cost of not taking the alternative.