Find the exit of this maze

 This is a riddle in the category think out of the box.

Find the exit of this maze.

You have to pass through colored orbs in order red, blue, red, blue, and so on.

Can you find the exit?

A Christmas card with a cryptographic twist for charity

This is a riddle in the category think out of the box.

News article - 7 Dec 2015

This year, along with his traditional Christmas cards, Director GCHQ Robert Hannigan is including a brain-teasing puzzle that seems certain to exercise the grey matter of participants over the holiday season.

The card, which features the 'Adoration of the Shepherds' by a pupil of Rembrandt, includes traditional Christmas greetings from Director on behalf of the department. However, unlike previous years, the 2015 card will contain a grid-shading puzzle and instructions on how it should be completed. By solving this first puzzle players will create an image that leads to a series of increasingly complex challenges.

10 people and random hats riddle

This is a riddle in the category math riddles.

 There are 10 people lined up from tallest to shortest each wearing a different hat color (black or white).

The entire group doesn’t know how many black or white hats there are and you can only see the people in front of you but you have to guess what color your hat is.

In fact, the entire group needs to guess 9 of the 10 hat colors correctly, starting from the tallest one.

Crazy cut

This is a riddle in the category logic riddles.

You are to make one cut (or draw one line) – of course it needn’t be straight – that will divide the figure into two identical parts?

Simple Algebra lessons...

This is a riddle in the category math riddles.

Simple Algebra lessons...

Complete the equation.

Only for Geniuses

This is a riddle in the category logic riddles.

100 pounds of potatoes

 This is a riddle in the category logic riddles.

 You have 100 pounds of potatoes, which are 99 percent water by weight.

 They dehydrate until they’re 98 percent water. 

How much do they weigh now?

Parking spaces...

This is a riddle in the category think out of the box.

What is the number of the parking space containing the car?

Coin flip winners

 This is a riddle in the category logic riddles.

 Alice and Bob are playing a game. They are teammates, so they will win or lose together. Before the game starts, they can talk to each other and agree on a strategy.

 When the game starts, Alice and Bob go into separate soundproof rooms – they cannot communicate with each other in any way. They each flip a coin and note whether it came up Heads or Tails. (No funny business allowed – it has to be an honest coin flip and they have to tell the truth later about how it came out.) Now Alice writes down a guess as to the result of Bob’s coin flip; and Bob likewise writes down a guess as to Alice’s flip.

 If either or both of the written-down guesses turns out to be correct, then Alice and Bob both win as a team. But if both written-down guesses are wrong, then they both lose.

The puzzle is this: Can you think of a strategy Alice and Bob can use that is guaranteed to win every time?

The mystery ball and 40 kilogram in the Balance

 You are given a mystery ball and are told that it has a whole-number weight between 1 and 40 kilogram (inclusive).

 You are then given a balance scale  and you are allowed to pick four weights, each weighing any whole-number amount. You must choose these weights so that no matter what the mystery ball weighs, you will be able to determine its weight using just the balance scale and these four weights.

What weights should you choose?

Row Your Trees

 This is a riddle in the category math riddles.

 How can seven trees be planted such that there are six rows of trees in straight lines consisting of three trees?

The 6 colored balls

 This is a riddle in the category logic riddles.

 We have 2 yellow, 2 red and 2 green balls. For each color, one ball is heavy and the other is light. All heavy balls weigh the same. All light balls weigh the same.

How many weighings on a beam balance are necessary to identify the three heavy balls?

Chameleons and the island

 This is a riddle in the category logic riddles.

 On an island live 13 green, 15 yellow and 17 red chameleons.

When two chameleons of different colors meet, they both change into the third color (for example if a red one meets a yellow one, they both change into green).

Is there a sequence of pairwise meetings after which all chameleons have the same color?

The string order

 This is a riddle in the category math riddles.

 Think of a 10-character string with the numbers 0 through 9 and each number appearing exactly once, such that each number (except for the first of the left number) is within 1 of SOME number to its left (e.g. we would say that 6 is within 1 of 5 and 7. Note that 0 is NOT within 1 of 9, i.e. we don't wrap around from 9 to 0).

 For example, 3452671089 is correct, because for any number in it (except for the 3 all the way on the left), you can find a number to its left that is with 1 of it. For example, if you look at the number "7", then you can find the number "6" to its left, which is within 1 of it.

Double Hearts Ratio Puzzle

 This is a riddle in the category logic riddles.

Which is bigger: the total area of orange or the total area of red?