Answer:
diminishing returns
Step-by-step explanation:
As the time in the swimming pool training increases the return (utility) of it decreases
while as the other disciplines has no time invested the utility of a single hour on in outweights the utility of the 20th hours in the swimming pool.
Becky is moving into other areas to increase their total utility as the swimming pool hours aren't as effective as before. Once Becky learned to swimm it makes a great difference than not knowng thus, the hours of training that skill are worthless utility now.