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 4 The Classic Weights & Scale You have 8 lead marbles, one of which is heavier than the rest. What is the minimum amount of “weightings” (i.e. with a see-saw scale) you need to do to guarantee finding the odd one out? Submitted by Valentin Doable 4.3 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 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 5 3 Brilliant People There are three genii standing in a row in a room facing the same direction. Thus, the genius at one end can see the two genii ahead of him, the genius in the middle can only see the one genius ahea ... Submitted by Ravi Doable 4.3 2 The North Pole Bear Puzzle Reloaded A man walks 1 mile south, then 1 mile east, and finally 1 mile north to find himself in exactly the same position as he started. He is NOT at the north pole, nor does he shoot a bear. Where is he? ... Submitted by Ravi Doable 6.0 4 Surgery A boy and his father get into an enormous and unfortunate car accident. The father is taken to one hospital and the son to another. The boy’s surgeon walks into the hospital room and says “I cannot ... Submitted by Valentin Doable 3.3 5 Cards With Crosses You have a stack of 23 cards. Each card has an image of a cross on one side, and an image of a circle on the other side. You know that 14 cards in the stack are laying with the cross up, and therefor ... Submitted by Valentin Doable 6.0 2 How far can you go? You have a 4 wheels car and a spare tire in the trunk. The tire being used will be worn off for 1/4 part of it per mile (completely wear out for 4 miles) How to make use of the spare tire to go as fa ... Submitted by MoralMachine Doable 5.2 2 Tick Tock With a seven-minute hourglass and an eleven-minute hourglass, what is the quickest way to time the boiling of an egg for fifteen minutes? Submitted by Aakash Easy 2.6 4 Its waistline is a hexagon Heart of Darkness, Coat of Grain, Was once alive, Now feels no pain, Never walks, but Leaves a Trail. Circle head and pointed tail. Grows shorter as the day goes on- Its waistline is a hexagon. Wha ... Submitted by Valentin Doable 5.2 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 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 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 5 Count The Bits Write a function that counts the number of bits in an integer that are set to 1 that is linear in time complexity in the worst case, but sub-linear on average. Submitted by Jay Elliott Hard 7.6 1 4 buttons and a light bulb There are two rooms, in one room there is a light bulb, and in the other there is a round table, with 4 buttons arragned in a square on it. Each button may be on or off, and the light bulb will be on o ... Submitted by TulkinRB Hard 8.0