Scenario 1: A salesperson introduces a mobile-data plan to Randy, which allows him to pay HK$800 per month and enjoy unlimited data usage. Randy said he is happy with the plan and is willing to subscribe to it.
a) Explain the above Randy's decision by using a graph/graphs based on the concept of marginal utility/happiness, consumer surplus and marginal cost.
(5 points)
Scenario 2: A salesperson introduces a mobile-data plan to Michael, which allows him to pay HK$200 per month and enjoy 20G of data usage. Michael said he is happy with the plan and is willing to subscribe to it. Note that Michael will use more than 20G of data when it is free-of-charge. (5 points)
b) Explain the above Michael's decision by using a graph/graphs based on the concept of marginal utility/happiness, consumer surplus and marginal cost.
(5 points)

Scenario 3: A salesperson introduces a mobile-data plan to Albert, which allows him to pay HK$200 per month and enjoy 20G of data usage. Albert said he is happy with the plan and is willing to subscribe to it. Then, the salesperson shows another plan to Albert, which allows him to pay HK$800 per month and enjoy unlimited data usage. Albert said he is also happy with the plan and is willing to subscribe it. Albert, however, decided to take the plan that costs HK$200 monthly and provides 20G of data usage after comparing the two plans. Similar to Michael in part b), Albert will use more than 20G of data when it is free-of charge.
c) Explain the above Albert's decision by using a graph/graphs based on the concept of marginal utility/happiness and consumer surplus and marginal cost. (10 points)