Career Guidance

Answers to Google Interview Questions

You are shrunk to the height of a nickel and thrown into a blender. Your mass is reduced so that your density is the same as usual. The blades start moving in 60 seconds. What do you do?

The blender question is real. Several Google interviewees recounted to me what happened when they came up against it. And though Google doesn’t comment on the specifics of its hiring process—it likes to maintain an air of mystery, which has led to a cottage industry of samizdat Google questions passed among hopeful future employees and curious outsiders—former and current Google HR specialists have shared rather freely with me what it is that motivates the way they interview job candidates.

We’ll get to the longer answer, but the short answer is that Google isn’t looking for the smartest, or even the most technically capable, candidates. Google is looking for the candidates who will best fit Google.

The blender riddle encapsulates the process of inventing a new product. You begin by brainstorming. There are many possible answers, and you shouldn’t be in a hurry to settle for the first idea that seems "good enough."

The two most popular serious answers to the blender riddle seem to be (1) lie down, below the blades and (2) stand to the side of the blades. There ought to be at least a nickel’s width of clearance between the whirring blades and the bottom or sides of the blender jar. Another common reply is (3) climb atop the blades and position your center of gravity over the axis. Hold tight.

None of the above answers scores you many points at Google. Former and current Google interviewers have told me that the best answer they’ve heard is: Jump out of the jar.

The question supplies an important clue: the word "density." "Being shrunk to the size of a nickel" is not a realistic predicament. For starters, it might mean eliminating 99.99% of the neurons in your brain. To deal with a question like this, you have to decide where to suspend disbelief.

The fact that the interviewer mentions a detail like density is a nudge. It says that things like mass and volume matter in this question and that a successful answer can use simple physics.

In short, if were you shrunk to 1/10 your present height, your muscles would be only 1/100 as powerful—but you’d weigh a mere 1/1,000 as much. All else being equal, small creatures are "stronger" in lifting their bodies against gravity. Were you shrunk to nickel size, you’d be strong enough to leap like Superman, right out of the blender. Think of the feats performed by fleas in a flea circus.

That is the kernel of a good answer to the question. But Google’s interviewers are not just looking for someone who has the basic idea. The best answers to many of the questions begin with, "It depends."

What’s the most efficient way to sort a million 32-bit integers?

It depends on the makeup of the list of integers and the constraints of time and memory. The applicant is expected to ask about these things. In general, Google is not trying to fill a particular job. The way the company morphs and grows, they want to find people who can join in one role and end up doing something completely different.

Google has tried biodata. "Did you ever make a computer from a kit?" was one question that the company found could isolate candidates with a lifelong passion for computers. But such methods have been de-emphasized in favor of its sometimes quirky interviewing process.

Design an evacuation plan for San Francisco.

Use a programming language to describe a chicken.

What is the most beautiful equation you have ever seen? Explain.

By design, none of these questions has a right answer. This has led to intense speculation and even paranoia among Google job candidates. It’s also led to other companies adopting Google-esque questions without having any idea what constitutes a good answer. Some more of google questions and the their answers are given below.

1. What’s the next number in this sequence: 10, 9, 60, 90, 70, 66 … ?

A. Spell the numbers out:

Ten

Nine

Sixty

Ninety

Seventy

Sixty-six

They are in ascending order, based on the number of letters in the spelled-out numbers. A correct response will have nine letters: 96, for instance. A cleverer answer is "one googol." That’s the huge number that can be written as a "1" with a hundred zeros after it. Google, the company’s name, was originally a misspelling of "googol."

2. You’re in a car with a helium balloon on a string that is tied to the floor. The windows are closed. When you step on the gas pedal, what happens to the balloon—does it move forward, move backward, or stay put?

A. The near-universal intuition is that the balloon leans backward as you accelerate. Well, the intuition is wrong. Your job is to deduce how the balloon does move and to explain it to the interviewer.

One good response is to draw an analogy to a spirit level. For the not so handy, a spirit level is the little gizmo carpenters use to make sure a surface is horizontal. It contains a narrow glass tube of colored liquid with a bubble in it. Whenever the spirit level rests on a perfectly horizontal surface, the bubble hovers in the middle of the tube. When the surface isn’t so level, the bubble migrates to the higher end of the tube. The takeaway here is that the bubble is simply a "hole" in the liquid. When the surface isn’t level, gravity pulls the liquid toward the lower end. This pushes the bubble wherever the liquid isn’t— toward the opposite end.

Untie the helium balloon and let it hit the moonroof. It becomes a spirit level. The balloon is a "bubble" of lower-density helium in higher-density air, all sealed in a container (the car).

Gravity pulls the heavy air downward, forcing the light balloon against the moonroof.

When the car accelerates, the air is pushed backward, just as your body is. This sends a lighter-than-air balloon forward. When the car brakes suddenly, the air piles up in front of the windshield. This sends the balloon backward. Centrifugal force pushes the air away from the turn and sends the balloon toward the center of the turn. Of course, the same applies when the balloon is tied to something; it’s just less free to move. The short answer to this question is that the balloon nods in the direction of any acceleration.

3. Using only a four-minute hourglass and a seven-minute hourglass, measure exactly nine minutes—without the process taking longer than nine minutes

A. Start both hourglasses at 0 minutes. Flip over the four-minute glass when it runs out (at 4:00); ditto for the seven-minute glass (at 7:00). When the four-minute glass runs out the second time (at 8:00), the seven-minute glass will then have one minute of sand in its lower bulb. Flip the seven-minute glass over again and let the minute of sand run back. When the last grain falls, that will be nine minutes.

4. A book has N pages, numbered the usual way, from 1 to N. The total number of digits in the page numbers is 1,095. How many pages does the book have?

A. Every page number has a digit in the units column. With N pages, that’s N digits right there. All but the first 9 pages have a digit in the tens column. That’s N – 9 more digits.

All but the first 99 pages have a digit in the hundreds column (accounting for N – 99 more digits).

I could go on, but not many books have more than 999 pages. A book with 1,095 digits in its page numbers won’t, anyway.

This means that 1,095 must equal:

N + (N – 9) + (N – 99).

This can be simplified to:

1,095 = 3N – 108.

That means that 3N = 1,203, or N = 401. That’s the answer, 401 pages.

5. A man pushed his car to a hotel and lost his fortune. What happened?

A. He was playing Monopoly.

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