How many trailing zeros are in the number 5! (5 factorial) **Asked to:** Systems engineer at Google

You have two light bulbs at a 100-story building. You want to find the floor at which the bulbs will break when dropped. Find the floor using the least number of drops. **Asked to:** Software engineer at Facebook

If you had 5,623 participants in a tournament, how many games would need to be played to determine the winner? **Asked to:** Manager at Amazon

There are 20 different socks of two types in a drawer in a completely dark room. What is the minimum number of socks you should grab to ensure you have a matching pair? **Asked to**: Software development engineer in test at Web trends

If you have a square room with no roof, and you had four flagpoles you had to plant on the walls so that each flagpole touched two walls, how would you do it? **Asked to:** Software engineer at Cisco

There are 9 balls all of which weigh the same except one, what is the minimum weighings necessary to find the ball weighs more (or less)? **Asked to:** Software engineer at DE Shaw & Co

You have 2 pieces of rope, each of which burns from one end to the other in 30 minutes (no matter which end is lit). If different pieces touch, the flame will transfer from one to the other. You cannot assume any rope properties that were not stated. Given only 1 match, can you time 45 minutes? **Asked to:** ASIC verification engineer at Zoran

In front of you are three light switches. Only one does anything, and it turns on the light downstairs. From here you can’t see the light, and it makes no sound. You must determine which switch operates the light, but you can only go check it once. How do you figure out which switch is for the light? **Asked to:** Software engineer at Raytheon