Friday, April 2nd, 2010
Let's say you drop a ball from the Leaning Tower of Pisa, which is 179 ft high, and it bounces back 10% of the dropped height - 17.9 ft. Then on the second bounce it bounces up 10% again - 1.79 ft, and so on for ever. How ...
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Friday, April 2nd, 2010
I read somewhere this is a Google interview question: Let's say you drop a stick, breaking it randomly in 2 places, leaving you with 3 smaller sticks. What's the probability you can make a triangle out of the 3 sticks?
[ddet Answer]
There are a number of ways to tackle this, including ...
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Sunday, February 21st, 2010
Say there are four bugs standing at the corners of an imaginary 1m * 1m square. Each of the bugs is facing the bug that is on the adjacent, clockwise corner from where they are.
At the same instant, each of the four bugs starts walking directly towards the bug they ...
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Thursday, December 31st, 2009
This is another probability question that seems straightforward but can be deceptive...
You're an FBI agent and have been monitoring a large gang, and you know that 1/4 of its members always tell the truth, the rest always lie. Then you get taken hostage by the gang, and two gang members ...
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Thursday, June 19th, 2008
Let's say you're contracted to build roads to connect four towns that are at the corners of an imaginary square with sides 1 mile. What's the shortest length of road system you can build so that every town can get to every other town?
[ddet Answer]
The first answers that ...
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Saturday, June 14th, 2008
It's 3 O'Clock. What will be the time when the minute and hour hands are next in the same position (coincident)?
[expand title=Answer]
The Plodder's way: Let's start with the minute hand at the 12 and hour hand at the 3. Let's call x the number of minute ...
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Saturday, June 14th, 2008
A few more brainteasers..
Some of these are from Heard on the Street - a book of interview questions for Quants I'm trying to get through. Well worth a read if you're into this sort of thing...
1. Two ropes of different lengths, and you know that if you were to ...
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Friday, June 13th, 2008
I'd blogged previously about rolling a die and being given whatever you roll in dollars. You get given two more chances if you don't like what you get the first time, or the second time, for a max of 3 rolls. What's your strategy? You can see the answer in ...
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Sunday, June 1st, 2008
Some probability questions/puzzles:
1. I have two children. One of my children is a girl. What are the chances I have two girls?
[expand title=Answer]
The answer to the question as stated is not 50/50. After being told that one of your children is a girl, you know there are 3 options (with ...
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Sunday, May 18th, 2008
The puzzle
You have 8 oranges - one is heavier than the others. How many weighings on a justice scale do you need to determine which one it is?
Answer
It's tempting to split the oranges in the middle, and weigh 4 and 4, which would take 3 weighings. But you ...
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