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 5 The Stealing Mailman This is a fairly simple problem that can cause some people trouble. Kevin and Sophia want to mail high confidential letters between each other. They know that the mailman is crooked and opens the le ... Submitted by Ravi Doable 6.5 6 Clever Commuter Every day, Fred takes the train to travel from his work back to Alkmaar, his place of residence. Usually, he arrives at the station of Alkmaar at six o’clock, and exactly at that moment he is picked ... Submitted by Valentin Hard 7.5 4 Left Hands Only Assume there are approximately 6,000,000,000 (6 billion) people on Earth. What would you estimate to be the result if you multiply together the number of fingers on every person’s left-hands? For t ... Submitted by Aakash Hard 6.8 2 The Easy Sum of 1..100? Quick,without using a calculator, what is the sum of all numbers between 1 and 100 inclusive? Or 1..10 for that matter.. Submitted by Valentin Easy 2.5 3 What number is next? What number comes next in this sequence? 4, 20, 56, 120, 220, ? Submitted by Aakash Doable 4.3 3 Power of 2 (Microsoft Interview) Given any number n, using one line of C (using no external libraries or functions) code, determine if n is a power of 2. Return 1 if n is a power of 2 and 0 if not. Submitted by Aakash Doable 6.0 5 A Pharmacist's Nightmare You have 5 jars of pills. Each pill weighs 10 gram, except for contaminated pills contained in one jar, where each pill weighs 9 gm. Given a scale, how could you tell which jar had the contaminated p ... Submitted by Ravi Hard 7.0 0 Cutting Numbers When is Seven half of Twelve? Submitted by Ravi Easy 3.0 0 Plane In The Wind An airplane flies in a straight line from airport A to airport B and back. It has constant engine speed and no wind. Will its total flight time increase, decrease or stay the same if throughout bot ... Submitted by Valentin Doable 4.0 2 Lockers A high school has a strange principal. On the first day, he has his students perform an odd opening day ceremony: There are one thousand lockers and one thousand students in the school. The princip ... Submitted by Aakash Hard 7.1 2 The Way Engineers Think A priest, a doctor, and an engineer were waiting one morning for a particularly slow group of golfers. Engineer: What’s with these guys? We must have been waiting for 15 minutes! Doctor: I don’t ... Submitted by Aakash Doable 6.0 4 Up and Down Explain the following scenario: A man lives on the twelfth floor of an apartment building. Every morning he takes the elevator down to the lobby and leaves the building. In the evening, he gets int ... Submitted by Valentin Hard 7.3 28 12 Identical Balls You have 12 identical balls. One of them is slightly different in weight than the rest. You have three weighs of a balance scale to determine which ball is different and whether it is heavier or li ... Submitted by Valentin Doable 6.2 1 Classic Knights & Knaves Raymond Smullyan has made a career of writing logic problems. His most famous have to do with a mythical island of Knights and Knaves. Knights always tell the truth, and Knaves always lie. As you a ... Submitted by Ravi Doable 5.5 7 Cooking Time A cook must put a souffle exactly 9 minutes at the oven, but he only have a 7 minutes hourglass and a 4 minutes hourglass. How can he measure 9 minutes with those clocks? Submitted by Ravi Doable 5.7