An article in the New York Times observes that 401(k) plans:

have largely supplanted traditional pensions and become the central pillar of America’s employer-sponsored retirement system, with 60 million workers participating in them.

a. What are “traditional pension plans,” and how do they differ from 401(k) plans?

b. Briefly explain why 401(k) plans might be more desirable to employers and employees than traditional pension plans. Are there any reasons why 401(k) plans might be less desirable to either group?