Quant, Math & Computer Science Puzzles for Interview Preparation & Brain Teasing
A collection of ~225 Puzzles with Solutions (classified by difficulty and topic)

Jun 17, 2014

Expected length of Last Straw - Breaking the back of a camel


Source: Puzzle Tweeter who took it from Mind your decisions

Problem: A camel is loaded with straws until it's back breaks. Each straw has a weight uniformly distributed between 0 and 1, independent of other straws. The camel's back breaks as soon as the total weight of all the straws exceeds 1. Find the expected weight of the last straw that breaks the camel's back.

Update (18th June 2014):
Solution posted by me (Pratik Poddar) in comments


Jun 16, 2014

Cards on a Square Turntable

Source: Steve Miller's Math Riddles

Problem:

A square has a quarter in each corner. You are blindfolded and must get all quarters to be heads up or all to be tails up. You will be told when you have done this. You may flip however many you want, then ask if you are done (this constitutes a turn). The square is then rotated/spun an undisclosed number of times. You then get another turn and so on…

Is there a strategy that is guaranteed to work in a finite number of moves, and if so, what is that smallest number of moves you need to be 100% you’ll be able to have all heads up or all tails up?

The same problem is there on the blog - in a different form - asked more than 50 months back :-) - Blind Flipping - CSE Blog