To determine which plan would be the best buy for Joe, we can calculate the total cost of each plan based on his estimated phone usage of 250 minutes per month.
Plan A-plus Phones:
Flat rate cost = $20
Cost of phone calls = 250 x $0.15 = $37.50
Total cost = $20 + $37.50 = $57.50
Plan Cell-o-fone:
Flat rate cost = $30
Cost of phone calls = 250 x $0.10 = $25.00
Total cost = $30 + $25.00 = $55.00
Based on these calculations, it appears that Plan Cell-o-fone would be the best buy for Joe, with a total cost of $55.00 compared to Plan A-plus Phones' total cost of $57.50. Even though Plan A-plus Phones has a lower per-minute rate, the higher flat rate cost makes it more expensive for Joe given his estimated phone usage.