Mia spent 10 hours studying for an exam, and she received an A on the exam. Normally, she would have spent that time watching TV instead of studying. Mia figures she could have made a B after studying only 5 hours, but she really wanted an A. What is Mia ’s marginal cost in terms of TV viewing to move from a B to an A on the exam?

Mia's marginal cost is 5 hours

Explanation:

Marginal cost can be seen as the change in total production cost if the output is increased by 1 more unit.

In this case, the marginal cost can be the additional benefit got, (which is a higher grade)  by putting in extra hours of study.

Since Mia can get an A which is the highest grade by putting in 5 hours of study, the extra 5 hours of study can be seen in economic terms as a wasted time resource. This is because there is no grade higher than an A.

Consider the formula

Marginal cost =

Let the cost in this case be the time it takes Mia to study (in hours)

Let the benefit be the additional grade i.e (from B to A) obtained for studying for 1 hour.

For mathematical purposes, let the movement from B to A have a value of 1 unit in terms of benefit

Marginal cost in this case will be  = = 5 hours

Any additional time invested will create infinite marginal costs because there is no grade increase  as shown below

Marginal cost for reading for 20 hours = = ∞

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