Though, they weren't responsible for the Black Plague, I'll give them that. Getting rid of the cats in that instance allowed the rats who did carry the plague to flourish. So, yeah, their useful if you need something killed.
Skill testing questions (or STQ) are a legal requirement attached to many contests in Canada.
The combined effect of Sections 197 to 206 of the Criminal Code of Canada bans for-profit gaming or betting, with exceptions made for provincial lotteries, licensed casinos, and charity events. Many stores, radio stations, and other groups still wish to hold contests to encourage more purchases or increase consumer interest. These organizations take advantage of the fact that the law does allow prizes to be given for games of skill, or mixed games of skill and chance. In order to make the chance-based contests legal, such games generally consist of a mathematical STQ.
The Promotional Contest Provision of the Competition Act also states that prizes are to be distributed "on the basis of skill or on a random basis."
The most common form that these questions take is as an arithmetic exercise. A court decision ruled that a mathematical STQ must contain at least three operations to actually be "skill testing"; for example, a sample question is "(2 × 4) + (10 × 3)" (Answer: 38). Enforcement of these rules is not very stringent, especially for small prizes; the player may not be required to answer the STQ to claim a prize. Anecdotally, getting the answer wrong is also often not an obstacle to claiming a prize. The questions are also becoming easier. For contests held in other countries but open to Canadians, an STQ must be asked of any potential Canadian winner.
The same section of law prohibits receiving consideration in exchange for playing the games, resulting in a related peculiarity of Canadian contests: the "free entry alternative", which is usually telegraphed by the fine print "No purchase necessary". Generally this means that it is possible to enter the contest for free by, for example, writing a letter to the entity sponsoring the contest and requesting a game piece or entry form.