Riddle: There are five acquaintances. One of them shot and killed one of the other five. Which man is the murderer? 1. Dan ran in the NY City marathon yesterday with one of the innocent men. 2. Mike considered being a farmer before he moved to the city. 3. Jeff is a top-notch computer consultant and wants to install Ben's new computer next week. 4. The murderer had his leg amputated last month. 5. Ben met Jack for the first time six months ago. 6. Jack has been in seclusion since the crime. 7. Dan used to drink heavily. 8. Ben and Jeff built their last computers together. 9. The murderer is Jack's brother; they grew up together in Seattle.
Answer: 1. Jack is not the murderer, because he is the brother of the murderer. 2. Dan can't be the murderer since he ran a marathon, and the murderer recently had his leg amputated, and wouldn't be running a marathon of any magnitude that quickly. 3. Ben is not the murderer if he just met Jack, since Jack and the murderer grew up together. 4. This leaves Jeff and Mike. Since Jeff is still alive (he wants to install a new computer next week, present tense) he must be the murderer. Mike also didn't grow up with Jack. It has been determined that Jack, Dan and Jeff are all alive. Ben must also be alive since Jeff plans to install Ben's computer next week. This means that Jeff killed Mike.