Beth is training for a triathlon, a timed race that combines swimming, biking, and running. consider the following sentence: because her pool sessions are her swim more quickly, beth plans to reduce by 1 hour per week the time she spends training on the bike and increase by 1 hour the time she spends in the swimming pool; however, her husband says that she should stop doing any biking and running and spend all 20 hours per week in the pool.

The basic principle of individual choice that Beth's plan illustrates and her husband's does not is that of marginal analysis.

Explanation:

Though Beth is planning to divide her time between the activities in a partial manner, she has still kept time for the other activities that are going to be the part of the triathlon. Thus, Beth can be said to have done a marginal analysis of the activities and the cost that they would bear as far as time is concerned. The advice given by Beth's husband does not leave room for marginal analysis as he wishes that she dedicates all her time for swimming alone.