|Spoiler Inside: Solution to Puzzle||SelectShow>|
Empress has 2 1/2 hours per day for entertainment.
There is no combination of mice and catnip that can total more than $20 so a guinea pig is necessary. Two guinea pigs would be three hours of entertainment and so not allowed. This makes the maximum so far 1 guinea pig, 2 catnip, and 2 mice which total 3 hours. 1/2 hour has to be removed.
This can be done only by removing one catnip or two mice. If the catnip is removed, the remainder adds to 2 1/2 hours, but is only $20. If the mice are removed, it is $21. The only way to arrange one guinea pig and two catnip with no two in a row is catnip – guinea pig – catnip.
There is exactly one entertainment program for Empress (catnip – guinea pig – catnip). Cats can be so hard to please.