Hello
reader! Welcome back!
What’s
your answer then?
Well,
in this article we have the answer for the question in our last post before.
Take
your time, hope you enjoy:
1.How
many golf balls can fit in a school bus?
Job:
Product Manager
Answer:
This is one of those questions Google asks just to see if the applicant can
explain the key challenge to solving the problem.
Matt
Beuchamp came up with a dandy answer, writing:
I figure a standard
school bus is about 8ft wide by 6ft high by 20ft long – this is just a guess
based on the thousand of hours I have been trapped behind school buses while
traffic in all directions is stopped.
That means 960 cubic
feet and since there are 1728 cubic inches in a cubit foot, that means about
1.6 million cubic inches.
I calculate the volume
of a golf ball to be about 2.5 cubic inches (4/3* pi * .85) as .85 inches is
the radius of a gold ball.
Devide that 2.5 cubic
inches into 1.6 million and you come up with 660,000 golf balls. However, since
there are seats and crap in there taking up space and also since the spherical
shape of a golf ball means there will be considerable empty space between them
when stacked, I’ll round down to 500,000 golf balls.
Which sound ludicrous. I
would have sptitballed no more than 100k. But I stand by my math.
Of course, if we are
talking about the kind of bus that George Bush went to school on or Barney
Frank rides to work every day, it would be half that... or 250,000 golf balls.
2.How
much should you charge to wash all the windows in Seattle?
Job:
Product Manager
Answer: This is one of
those question where the trick is to come up with an easier answer than the one
that’s seemingly being called for. We’d say “$10 per window”.
3.In
a country in which people only want boys...
...every
family continues to have children until they have a boy. If they have a girl, they have another child. If they have a
bout, they stop. What is the proportion of boys to girls in the country?
Job:
Product Manager
Answer: This one caused
quite the debate, but we figured it out following these steps:
Imagine you have 10
couples who have 10 babies. 5 will be girls. 5 will be boys. (Total babies
made: 10, with 5 boys, 5 girls) The couples who had girls will have 5 babies. Half
(2.5) will be girls. Half (2.5) will be boys. Add 2.5 Boys to the 5 already
born and 2.5 girls to the 5 already born. (Total babies made: 15, 7.5 boys, 7.5
girls)
The 2.5 couples that had
girls will have 2.5 babies. Half (1.25) will be boys and half (1.25) will be
girls. Add boys to the 7.5 boys already born and girls to the 7.5 girls already
born. (Total babies: 17.5 with 8.75 boys and 8.75 girls).
And so on, maintaining a
50/50 population.
4.
How many piano tuners are there in the entire world?
Job:
Product Manager
Answer: We’d answer “However
many the market dictates. If piano need tuning once a week, and it takes an
hour to tune a piano and a piano tuner works 8 hours a day for 5 days a week 40
piano need tuning each week. We’d answer one for every 40 pianos.”
On Wikipedia, they call
this a Fermi problem.
The classic Fermi problem, generally attributed to Fermi, is “how many piano tuners are there in
Chicago?” A typical solution to this problem would involve multiplying together
a series of estimates that would yield the correct answer if the estimates were
correct. For example, we might make the following assumptions:
1. There are
approximately 5,000,000 people living in Chicago.
2. On average, there are
two person in each household in Chicago.
3. Roughly one household
in twenty has a piano that is tuned regularly.
4. Piano that are tuned
regularly are tuned on average about once per year.
5. It takes a piano
tuner about two hours to tune a piano, including travel time.
6. Each piano tuner
works eight hours in a day, five days in a week, and 50 weeks in
a
year.
From the assumptions we
can compute that the number of piano tunings in a single year in chicago is
(5,000,000 person in
Chicago) / (2 person/ household) x (1 piano/ 20 households) x (1 piano tuning
per piano per year) = 125,000 piano tunings per year in Chicago.
And we can similarly
calculate that the average piano tuner performs
(50 weeks/ year) x (5
days/ week) x (8 hours/day) x (1 piano tunings per year per piano tuner) = 125
piano tuners in Chicago.
A famous example of a
Fermi-problem-like estimate is the Drake equation, which is seeks estimate the
number of intelligent civilizations in the galaxy. The basic question of why,
if there are a significant number of such civilizations, ours has never
encounter any other is called the Fermi paradox.
5.Why
are manhole covers round?
Job:
Software Engineer
Answer: So it doesn’t
fall through the manhole (when plane ordinarily flush with the plane of the
street goes perpendicular to the street.)
6.Design
an evacuation plan for San Francisco
Job:
Product Manager
Answer: Again, this one
is all about the interviewer seeing how the interviewee would attack the
problem. We’d start our answer by asking, “what kind of disaster are we
planning for?”
7.How
many times a day does a clock’s hands overlap?
Job:
Product Manager
12:00
1:05
2:11
3:16
4:22
5:27
6:33
7:38
8:44
9:49
10:55
12:00
1:05
2:11
3:16
4:22
5:27
6:33
7:38
8:44
9:49
10:55
8.Explain the significance of “dead beef”
Job: Software Engineer
Our
(wrong) answer: Beef is always dead. Calling something "dead beef" is
redundant - a no-no for coders.
The
actual answer, NO ANSWER (We not sure yet):
DEADBEEF is a hexadecimal value that has was used in debugging
back in the mainframe/assembly days because it was easy to see when marking and
finding specific memory in pages of hex dumps. Most computer science graduates
have seen this at least in their assembly language classes in college and
that's why they expect software engineers to know it. From wikipedia:
"0xDEADBEEF ("dead beef") is used by IBM RS/6000
systems, Mac OS on 32-bit PowerPC processors and the Commodore Amiga as a magic
debug value. On Sun Microsystems' Solaris, it marks freed kernel memory. On
OpenVMS running on Alpha processors, DEAD_BEEF can be seen by pressing
CTRL-T.[3]"
9.A man pushed his car to a hotel and lost his
fortune. What happened?
Job: Software Engineer
Answer:
He landed on Boardwalk. (Painful, right?)
10.You need to check that your friend, Bob, has your correct
phone number…
…, but you cannot ask
him directly. You must write the question on a card which and give it to Eve
who will take the card to Bob and return the answer to you. What must you write
on the card, besides the question, to ensure Bob can encode the message so that
Eve cannot read your phone number?
Job: Software Engineer
Answer: Since you are just "checking,"
you ask him to call you at a certain time. If he doesn't, he doesn't have your
number.
Too simple? A suggestion: "
11.You’re the captain of a pirate ship...
...and your crew gets to vote on how the gold is divided up.
If fewer than half of the pirates agree with you, you die. How do you recommend
apportioning the gold in such a way that
you get a good share of the booty, but still survive?
Job: Engineering Manager
Answer: You divide the booty evenly between the top 51% of the crew.
12.You have eight balls all of the same size…
…7 of them weigh the
same, and one of them weighs slightly more. How can you find the ball that is
heavier by using a balance and only two weighings?
Job: Product Manager
Answer:
Take 6 of the 8 balls and put 3 on
each side of the scale. If the heavy ball isn't in the group of 6, you know
it's one of the remaining 2 and so you put those two in the scale and determine
which one. If the heavy ball is in the 6, you have narrowed it down to 3. Of
those 3, pick any 2 and put them on the scale. If the heavy ball is in that
group of 2, you know which one it is. If both balls are of equal weight, then
the heavy ball is the one you sat to the side.
13.You are given 2 eggs…
…You have access to a 100-story building. Eggs
can be very hard or very fragile means it may break if dropped from the first
floor or may not even break if dropped from 100th floor. Both eggs are
identical. You need to figure out the highest floor of a 100-story building an
egg can be dropped without breaking. The question is how many drops you need to
make. You are allowed to break 2 eggs in the process.
Job: Product Manager
Answer: The maximum egg drops for this method is 14
times.
Instead of partitioning the floors by 10, Start at the 14th floor, and then go
up 13 floors, then 12, then 11, then 10, 9, 8, 7, 6, 5, 4 until you get to the
99th floor, then here. If the egg were to break at the 100th floor, it
would take 12 drops (or 11 if you assume that it would break at the 100th
floor). Say, for example, that the 49th floor was the highest floor, the
number of drops would be the 14th, 27th, 39th, 50th (the egg would break on the
50th floor) plus the 40, 41,42,43,44,45,46,47,48, and 49th floor for a total of
14 drops.
14.Explain a database in three sentences to your
eight-year-old nephew.
Job: Product Manager
Answer: The point here is to test the
applicant's ability to communicate complex ideas in simple language. Here's our
attempt, "A database is a machine that remembers lots of information about
lots of things. People use them to help remember that information. Go play
outside."
15.You are shrunk to the height of a nickel…
… and your mass is proportionally reduced so as
to maintain your original density. You are then thrown into an empty glass
blender. The blades will start moving in 60 seconds. What do you do?
Job: Product Manager
Answer: This one is all about the judging
interviewee's creativity. We'd try to break the electric motor.
What do you think about it? Please do comment us!
