Four friends A, B, C, D Need to cross a bridge.. A maximum of 2 people can cross at a time.. It is night and they have just 1 lamp. People that cross the bridge must carry the lamp to see the way.. A pair must walk together at the speed of … [Continue reading]

## Supersonic bee

Two trains enter a tunnel 200 miles long, traveling at 100 mph at the same time from opposite directions. As soon as they enter the tunnel a supersonic bee flying at 1000 mph starts from one train and heads toward the other one. As soon as it reaches … [Continue reading]

## Palindrome dates

This year on October 2, 2001, the date in MMDDYYYY format will be a palindrome (same forwards as backwards). 10/02/2001 When was the last date that this occurred on? … [Continue reading]

## Daughter’s ages

Two MIT math grads bump into each other at Fairway on the upper west side. They haven't seen each other in over 20 years. The first grad says to the second: "how have you been?" Second: "great! i got married and i have three daughters now" First: … [Continue reading]

## Red and blue marbles

You have two jars, 50 red marbles and 50 blue marbles. You need to place all the marbles into the jars such that when you blindly pick one marble out of one jar, you maximize the chances that it will be red. When picking, you'll first randomly pick a … [Continue reading]

## Ants on a triangle

There are three ants on a triangle, one at each corner. At a given moment in time, they all set off for a different corner at random. What is the probability that they don't collide ? … [Continue reading]

## Balls in a bag

You have 20 blue balls and 14 red balls in a bag. You put your hand in and remove 2 at a time. If they're of the same color, you add a blue ball to the bag. If they're of different colors, you add a red ball to the bag. (assume you have a big supply … [Continue reading]

## Calendar cube

A man has two cubes on his desk. Every day he arranges both cubes so that the front faces show the current day of the month. what numbers are on the faces of the cubes to allow this? … [Continue reading]

## Zeroes in 100 factorial

How many trailing zeroes are there in 100! (100 factorial) ? … [Continue reading]

## Average salary

Three coworkers would like to know their average salary. How can they do it, without disclosing their own salaries to other two? … [Continue reading]