First, draw out a 10x10 grid. Take the shape below and see how many you can fit in the 10x10 grid. It should take up 6 grid squares. Also, it can be rotated. 1) How many can you fit in the grid? 2) Can you prove that this is the most possible?

Six-digit lottery ticket numbers are considered lucky if the sum of the first three numbers is equal to the last three. Eg. 123204, 871529... Prove that all possible lucky numbers added together is divisible by thirteen.

Let's say that you have a chessboard (they are 8x8 spaces) with a rook on it (only moves horizontally & vertically). You can put walls horizontally or vertically between the spaces. If the rook can get to every possible space on the chessboard without going over a wall, then it is a good chessboa...

But the puzzle is supposedly "Why are those numbers in that order?" 8, 18, 11, 15, 5, 4, 14, 9, 19, 1, 7, 17, 6, 16, 10, 13, 3, 12, 20, 2 Any ideas?

The answer to the riddle is two words. The Riddle: I grow by consuming one thing The more I consume the larger I get Regardless of my size you don't see more of me I am lighter than what I consume

Here is a code with symbols as hints (Note: The footnote on the second page has nothing to do with the puzzle, it's just there for copyright purposes): I am psyched to find out if or how somebody cracks it (there are two paths to the solution). The solution is the title of a movie. Have fun!

I know a word. It contains 6 letters. Take away a letter, and 12 remain. What is the word?

Soon after arriving to work this morning, I sent an email off to my pal over in IT upon realizing that my workstation wasn't fully functional. We both like to solve puzzles in our spare time, so rather than reveal precisely what I was expecting from him, I let him work it out for himself. Hey...

I have keys but no locks. I have a space but no room. You can enter, but can’t go outside. What am I?

I have a wooden snake puzzle in my collection that has been unsolved for years. I wondered if any of you might be interested. I have fiddled with it, but think it might need dynamic programming or something to solve. But maybe some of you have an approach that would work. The puzzle is pictured ...

15 pawns are placed on the centers of distinct squares of a chessboard. Prove that there are three pawns which form a right triangle. In the example board below, a couple of right triangles are illustrated. There are many others, but you only need to prove that one right triangle exists for...

Try to get as many numbers you can from 1-100, only using numbers that are also a number upside-down. Each number can be used only once, and any operations are allowed. (Examples: 0, 1, 6, 8, 9, 10, 16, 18, so on.) Try not to post numbers others have already done, focus on getting new ones.

I can only live where there is light, but I die if the light shines on me. What am I?

Alfred C. Bacon, an avid puzzler, has been kidnapped! Fortunately, we were able to find where he was being held. Unfortunately, he was no longer there. Fortunately, he left us a note, letting us know that he was safe, (although not necessarily happy). Fortunately, he let us know that he had encod...

How i can walk on these 7 bridges without walk on one of them twice?