Archive for April, 2010
Friday, April 30th, 2010
Here's two classic birthday puzzles:
How many people do you need in a room to have a better than 50% chance of finding at least one shared birthday among them?
[ddet Answer]
Like a lot of these problems, it's easier to first find the chances of the proposition not happening - ...
Posted in puzzles | 2 Comments »
Thursday, April 29th, 2010
You deal the first 13 cards from a well shuffled, 52-card deck to someone. What are the chances the 13 cards you deal are of the same suit?
[ddet Answer]
There's a couple of ways to do this - both incorporate useful techniques for solving these kind of problems.
The first way ...
Posted in puzzles | 1 Comment »
Sunday, April 25th, 2010
Let's say you're playing a coin-tossing game. You start with $10 and are looking to double your money. The game is very simple: you pick an amount to wager on each toss, and if you toss heads you win the amount you wagered (as well as keeping ...
Posted in puzzles | 1 Comment »
Friday, April 23rd, 2010
Let's say that you're playing a coin-tossing game, and you start with $1. You keep tossing forever, winning $1 if you toss heads, and losing $1 if you toss tails. What are the chances you'll eventually go bust (get to $0)? What are the chances you'll ...
Posted in mathematics, puzzles | 1 Comment »
Sunday, April 11th, 2010
Let's say you need to find out the highest floor in a 100 story building from which you could safely drop an egg without it breaking. What's your strategy to minimize the maximum (worst case) number of drops you have to try?
If you just had one ...
Posted in puzzles | 2 Comments »
Saturday, April 10th, 2010
I want to revisit a probability puzzle from a previous post: see problem #5 in http://rebrained.com/?p=20
You play a game where you alternate tossing a coin with a friend, and the first person to toss heads wins. But let's make it a little more interesting by making the coin ...
Posted in puzzles | No Comments »
Wednesday, April 7th, 2010
Let's say there are 100 people, including you, waiting to board a fully booked flight, each with an assigned seat. The first person to board doesn't pay any attention to his assigned seat, and sits somewhere at random. Each of the subsequent people will sit in their ...
Posted in puzzles | 2 Comments »
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 ...
Posted in mathematics, puzzles | No Comments »
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 ...
Posted in puzzles | No Comments »