Our group proposes a new 'donut question' nearly every week. The last person to get the answer is in charge of bringing the donuts for the next meeting. These are often often logic, math or science puzzles, though once in a while a sequence question may appear…

By moving only a single digit or sign, make the following equation valid.¹⁾ 62 - 63 = 1 Answer

There is a chef famous for his 9 minute boiled egg. Sadly, his 9 minute hourglass broke one morning. He looks around the kitchen and finds two hourglasses: one has 4 minutes worth of sand in it, the other has 7. Is there a way for the chef to measure 9 minutes using these two hourglasses? ²⁾

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There were 2 Bedouins in the desert: one had 5 loaves of bread, the other had 3. Another Bedouin meets them and wishes to share a meal with them. He has money, but no bread. They split the bread evenly and sit down to eat. After the meal, the third Bedouin thanks them and leaves them with 8 gold coins. How can the two split the money fairly? ³⁾

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“Semiprimes are highly useful in the area of cryptography and number theory, most notably in public key cryptography, where they are used by RSA and pseudorandom number generators such as Blum Blum Shub. These methods rely on the fact that finding two large primes and multiplying them together (resulting in a semiprime) is computationally simple, whereas finding the original factors appears to be difficult. In the RSA Factoring Challenge, RSA Security offered prizes for the factoring of specific large semiprimes and several prizes were awarded. The most recent such challenge closed in 2007.” (http://en.wikipedia.org/wiki/Semiprime#Applications)

For a simple example, find the prime factorization of the semiprime number 391. ⁴⁾

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Draw this design without retracing lines, no overlapping lines and without lifting your pen. ⁵⁾

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Treating each line as a matchstick that can be picked up and moved, make the following equation equal to 4 by moving only a single stick. ⁶⁾

   | + || + ||| + ||||

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Gauss could famously add a large number of consecutive digits from a young age. For this question, sum all the digits of each number from 1 - 1 million. As a brief example, consider the numbers 1-10. ⁷⁾

  1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 1 + 0 = 46

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One night, there were 4 people that came across a bridge they must cross. Because the bridge was very old an full of holes, it was impossible to cross in the dark. Luckily, there was a single flashlight which they must carry with them as the cross the bridge. The bridge also had a weight limit and would collapse if more than two of the people tried to cross at the same time.

Each person walked at a different speed and so when two traveled together, they would both walk the same speed as the slower of the two. Their speeds are as follows:
Person 1 will take 1 minute to cross the bridge.
Person 2 will take 2 minutes.
Person 3 will take 5 minutes.
Person 4 will take 10 minutes.

What is the shortest amount of time it will take to get all 4 people across the bridge? ⁸⁾

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Using the 8 digits 4 4 3 3 2 2 1 1, create an 8 digit number in which there is 1 digit between the two 1's, 2 digits between the two 2's, 3 digits between the 3's and 4 digits between the 4's. ⁹⁾

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If you were to rotate the year 1881 180 degrees, it would still read 1881. What in the next year after 1881 that will also read the same after being rotated 180 degrees? ¹⁰⁾

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What are the next two letters in this sequence? ¹¹⁾

   W A T N T L I _ _

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A man had three sons. One day, he was visiting with a friend of his. The friend asked how old his sons were, and the man responded by giving him clues about their ages. First, he told the friend that the product of his sons ages was 36. Next, he said the sum of their ages was the same as the friends house number. The man then said that the eldest son played the theremin. Using these three clues, the friend was able to figure out each sons age. Can you? ¹²⁾

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Using the digits 8,8,3 and 3 once each, create an expression that equals 24. You may only use subtraction, addition, multiplication and division. ¹³⁾

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The sundial is the timepiece with the fewest moving parts. What timepiece has the most moving parts? ¹⁴⁾

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The square piece of paper shown below has a hole cut out of it. With only a single cut, find a way to cut and recombine the paper so the hole is in the center of the paper. ¹⁵⁾

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How can you speak in English for a full minute without using the letter 'a'? ¹⁶⁾

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How many different ways can you arrange four colors in this pattern without having adjacent colors? ¹⁷⁾

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Choose five number that, when added in pairs, will sum to each of the values 0 1 2 4 7 8 9 10 11 12. ¹⁸⁾

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A man must visit his grandma. It will take him six days to make the trip. A person can only carry four days worth of food. How will he survive? ¹⁹⁾

Rules: The man must arrive at his grandma's home. There is no food between his house and his grandma's. He can bring other people with him, but no one is allowed to die. If other people come with him, they do not have to arrive at the grandma's home. Since no one is allowed to die, at the end of the trip everyone must either be at their own home, or at the grandma's home.

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Three men take part in a dual. The shooting order is predetermined: Jack shoots first, followed by Jerry, then John. If there are still men alive after one round of shooting, they continue to shoot in this order until only one man is left alive.

Jack is a poor shot, and only has a 1/3 chance of hitting his target. Jerry is better; he has a 2/3 chance of hitting his target. John is the best and has a 100% chance of hitting his target.

As Jack pulls out his pistol, he is unsure of who he should shoot at first. Where should he shoot to give himself the best chance of survival? ²⁰⁾

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What can you hold in your left hand that you cannot hold in your right hand? ²¹⁾

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²²⁾

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The maker doesn't need it, the owner doesn't want it, and the user doesn't know he is using it. What is it? ²³⁾

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A solid white cube is painted black. The cube is then cut into 125 equally sized smaller cubes. How many of these smaller cubes have black paint on at least 2 surfaces? ²⁴⁾

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Start with 12 toothpick arranged as above. Moving only 3, can you form 3 squares? ²⁵⁾

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