Job Search Tip of the Week – 10/13/2016


How to Ace Your First-Round (or really, Just about Any) Interview

Think like an Interviewer – Q5

This is post No. 3 of our our 19-post series which was inspired by this infographic (Check out our tips on how to effectively respond to “If you were shrunk to the size of a pencil and put in a blender, how would you get out?” and “Why should I hire you?”).

Contrary to what the above cartoon suggests, interviewers don’t ask “Why are manhole covers round” to trip you up – There’s method in their madness, so to speak.

“Why are manhole covers round?” became a popular interview question since Microsoft reportedly began using it a decade ago in order to identify the job candidates who think outside-the-box.

That being said, interviewers are looking for more than just creativity. “Why are manhole covers round?” and other definitional questions are meant to reveal your thinking process, most specifically your deductive reasoning and lateral thinking skills.

So sadly, “Manhole covers are round because if they weren’t the Teenage Mutant Ninja Turtles couldn’t spin really fast and fit down the hole to go home,” (one of my favorite answers to this question, said in all seriousness by a five-year-old), probably wouldn’t land you that second interview. Because although creative, it lacks logic.

Thus, when responding to “Why are manhole covers round” and questions of the like, it’s important to remember that you’re being evaluated not for your answer but how you approached the problem and got to your answer.

In other words: Are you willing to entertain a “silly” question with seriousness? Can you look at a problem from many angles? Can you think logically? Is there a method to which you consider, accept, or reject plausible solutions before proposing one?

Engaging in deductive reasoning, or “top-down” logic, will get you there. It’s the process in which a specific, logical conclusion is derived from one or more general premises that are assumed to be true. There are three forms of deductive reasoning:

  • Law of detachment. Better known as the if-then statement: If P is satisfied, then Q exists.
    Basic Form: P –> Q (conditional statement). P (hypothesis stated). Q (conclusion deduced).
    Example: If the manhole is round, then the manhole cover is round (P –> Q). The manhole is round (P). There, the manhole cover is round (Q).
  • Law of syllogism. Or as I like to call it, “guilty by association.” It’s the forming of a conclusion by combining the hypothesis (P) of the first conditional statement with the conclusion of the second conditional statement.
    Basic Form: P –> Q. Q –> R. Therefore, P –> R. (You mathematicians will recognize it as an example of the transitive property (A=B. B=C. Therefore A=C.).
    Example: If you’re in the United States, then the manholes will be round (P –> Q). If the manholes are round, then the manhole covers will be round (Q –> R). Therefore, if you’re in the United States, then the manhole covers will be round (P –> R).
  • Law of contrapositive. Given a conditional statement, if the conclusion is false, the hypothesis must be false also. Think of it as working backwards!
    Basic Form: P –> Q. ~Q. Therefore, we can conclude ~P.
    Example: If the manhole is round, then the manhole cover is round (P –> Q). The manhole is not round (~Q). Therefore, the manhole cover is not round (~P).

Deductive arguments are evaluated for their validity and their soundness. You have validity if you affirm the premises and the conclusion, or deny the premises and the conclusion. In other words, you cannot ever have true premises and a false conclusion, or vise versa. You have soundness if your argument is valid and your premises are in reality true.

The example I provided for you in the “Law of syllogism” section also exemplifies a valid but not sound argument – Triangular manhole covers can be found in Nashua, New Hampshire to point in the direction of the underlying water or sewage flow, and also in Hamilton, Bermuda and San Francisco. There are also square or rectangle manhole covers. So because the first premise (P –> Q) is in reality false, it cannot be sound. However, it is a valid argument if you assume both premises to be true, or don’t know any better to say otherwise.

By the way, bonus points for you if you can address all aspects of the problem. For example, in regards to “Why are manhole covers round,” not all manhole covers are round (See above.). So the question then becomes, Why are the manhole covers that are round, round?

Here are the most commonly proposed explanations1 (I strongly encourage you to flex your creative muscle and either expand upon the ideas presented or refute them, rather than simply regurgitating them in an interview.):

  • If you’re considering only the round manhole covers, they are round by definition. So they are round because they are round. If you’re considering the value of a round manhole over any other shape…
  • Circles are more aesthetically pleasing in-between the straight lines and edges of the road.
  • A round manhole cover can’t fall through a hole that’s smaller than it, no matter what angle you turn it (Although it would suck to drive over it. In addition, a manhole cover in the shape of a Reuleaux triangle or any other polygon of constant width would also serve this purpose.).
  • Round manhole covers don’t need to be rotated to align properly with the shape of the manhole (if cut precisely), unlike triangles, squares, or rectangles.
  • You can lock a manhole cover into place simply by turning it if 1) it’s round and 2) if there’s a notch, rather than bolting it down or making the cover very heavy so that traffic passing over them doesn’t lift it up by suction (A shape with edges gets dislodged more easily when pressure is applied to one of its corners.). It thus uses less materials and costs less.
  • It’s easier and more accurate to manufacture steel into a circle than any other shape.
  • A round manhole cover has a smaller surface than a square one (Reminds me of Ledo’s Pizza slogan – “We’re square because we don’t cut corners!”), and thus is made of less material and consequently incurs less cost to make.
  • Round manhole covers require less manpower and lifting to move. (Rolling, rolling, rolling!).
  • Cylinders are the strongest shape against the earth’s compression. Pipes are cylindrical, so it’s only natural that the manhole used to put the pipes into the ground is round, and that the cover for the manhole also assumes a circular shape.
  • The term “manhole” implies that the hole must be large enough for a man (or a woman) to pass through. Humans are roughly cylindrical in shape. So the hole and its cover should be too.

    Remember: Often times, the problem has many possible solutions and there isn’t a “right” one, but rather ones that are more “right” than others. Consider the problem from many perspectives, develop possible explanations, and then effectively communicate how you (Logically!) arrived at the most plausible solution.

    Try Out Deductive Reasoning with Another Problem: If a tree falls in a forest and no one is around to hear it, does it still make a sound? (Hint: Your answer depends on your definition of the word “sound.”)

    Blogging Forward,

    Cartoon Credits: Implementing Scrum, David Farley
    1Some responses published on Wikipedia