Using marginal analysis, it can be said that, buying another economic textbook does not add to many benefits, as the student already has one economic textbook. Studying one textbook would give him the same benefit, then by studying another textbook. Buying another textbook does not add marks, but it certainly adds some marginal cost.

On the other hand, the movie will add to the pleasure of watching it and certainly gives additional benefit. Watching a movie is the marginal benefit of entertainment. Hence considering the cost-benefit approach of marginal analysis, the choice of going to movie adds marginal benefit and hence rational.