Red and Green Quiz | Brain Teasers

Quiz Answer Key and Fun Facts

1. Alice and Bob are each given either a red or a green card, which only they can see. They are told that at least one of their cards is red. Alice says to Bob, "I don't know what color your card is". Bob replies, "one of us is holding a red card, and the other one is holding a green card". What color is Bob's card?

Answer: Green

If Alice was holding a green card, she would know Bob must be holding a red card, as at least one of the cards is red. As she says "I don't know what color your card is" to Bob, she must be holding a red card.

Bob works this out and looks down at his own card. He says that between them there is one red and one green card. That means his card must be green.

2. Out of "red" and "green", don't choose the answer that isn't the opposite of the color that is not green.

Answer: Green

The color that is not green is red. The opposite of red is green. The color that isn't green is red. So we mustn't choose red, and the answer is green.

The sentence contains four negatives: "don't", "isn't", "opposite" and "not". Each pair of negatives cancel each other out, and the color mentioned as the subject is "green". The answer would be "red" if there were an odd number of negatives, but it is "green" because there are an even number.

3. Alex is holding either a red or a green card. Exactly three of the following people are telling the truth. Brooke: The card is red. Caitlin: Exactly one of Brooke and Derek is telling the truth. Derek: The card is green. Ethan: Caitlin is lying. Frankie: Ethan is lying. Georgia: The card is red. What color is Alex's card?

Answer: Green

Because Alex is holding either a red or green card, Brooke or Derek (and not both) is telling the truth. This makes Caitlin's statement true, and one of their statements true, so exactly one other statement is true.

Ethan's statement is false, as Caitlin's is true, and hence Frankie's statement is true. This must be the only other true statement, so Georgia is lying and the card is green.

4. The alphabetical position of the middle letter in this word is the number of letters in the word. Which color am I talking about?

Answer: Green

The middle letter in "green" is "e", and "e" is the fifth letter of the alphabet. "Green" is five letters long.

"Red" also has "e" as its middle letter, but it is only three letters long.

5. Most chessboards have light and dark-colored squares, but mine is a checkerboard of alternating red and green squares. In chess, a bishop moves diagonally, and a knight moves in an L shape (of any orientation). During a game, my bishop starts on a red square and makes a move. My opponent's knight starts on a green square and makes a move. What color square are both the bishop and knight on now?

Answer: Red

Diagonal lines on a checkerboard pattern are the same color. So a bishop currently on a red square can only move to other red squares.

In contrast, if you move in an L shape then you are moving two squares in one direction (horizontal or vertical) and then one square in the perpendicular direction (vertical or horizontal). Moving two squares from a green square, you will pass over a red square onto another green square; then moving one square will take you to a red square.

In chess, the fact that bishops always remain on the same color complex and knights alternate color each time they move is very important in understanding whether knights or bishops (generally of roughly equal strength) are more or less powerful than normal in particular positions.

6. I sit around a circle of seven people, and hold a double-sided counter with red on the face-up side and green on the obverse. I pass it around the circle, and as each person takes the counter they flip it to the opposite side. When it reaches me again, I pass it around the circle in the other direction, and we continue the pattern of flipping it during each pass. When I hold the counter for the third time, what color is face-up?

Answer: Red

We each pass the counter twice, once in each direction, so the number of flips is even (more precisely, 2*7 = 14), and the counter ends up in its original orientation, with red face-up.

This is true even if we change the number of people in the circle from seven to any other (positive integer) number.

7. A blue trapezium, green pentagon and red hexagon must be placed in a row from left to right according to the following rules: 1. The trapezium must not be to the left of the pentagon. 2. The pentagon must be to the left of the hexagon. 3. The hexagon must be to the left of the trapezium. What color shape is on the left?

Answer: Green

The factorial function in maths tells you how many ways there are to order n objects. In this case, we have 3! = 3*2*1 = 6 ways to order the objects, but the three rules make 1 ordering uniquely correct. If we added another item, there would be 4! = 4*3*2*1 = 24 ways to order the four objects, and so on.

If RGB refers to the (R)ed hexagon, (G)reen pentagon and (B)lue trapezium placed in that order from left to right, then the six possible orderings - and the rules which they violate - are:

RGB - rule 2
RBG - rule 1, rule 2
BRG - rule 1, rule 2, rule 3
BGR - rule 1, rule 3
GBR - rule 3
GRB - no rules

Therefore, the green pentagon is on the left (and the red hexagon is in the middle, and the blue trapezium on the right).

Notice that for each rule, half of the possible orderings will violate the rule, and half will not, by symmetry.

8. A card has writing on both sides. One side reads, in red ink, "the statement on the obverse is a lie". The obverse reads, in green ink, "the statement on the obverse is true if and only if it is written in ___". To make this a paradox (where there is no consistent way to call some of the statements "true" and some of them "false"), what color fills in the blank?

Answer: Red

Let's fill in the blank with the color "red". Then, if the first side is true then the other side is a lie, so the first side is not written in red, a contradiction. So the first side is a lie, and the other side is true; but as the first side is written in red that means that it is a true statement, a contradiction.

If we filled the blank with "green" then there are two consistent interpretations of the statements: that the first side is true, or the obverse is true, but not both. This is a strange situation, but not a paradox by the definition given.

9. Six people at a table play a game. They begin with a red and a green counter each. The first player puts a red counter into a collective pile, which is passed onto the next player. Each subsequent player adds their red counter if and only if there was an odd number of green counters in the pile at the beginning of their turn, and adds their green counter if and only if there was an odd number of (total) counters in the pile at the beginning of their turn. So, each player's turn could consist of adding both a red and a green counter, or one or the other, or neither, before passing the new pile onto the next player. When the sixth player has completed their turn, what color are the majority of the counters?

Answer: Red

After the first player's turn, there is a single red counter and no green counters in the collective pile, which we will record as 1-0.

The second player adds a green counter, to bring the score to 1-1.
The third player adds a red counter, yielding 2-1.
The fourth player adds a counter of each color, to give 3-2.
The fifth player adds a green counter, so the score is 3-3.
The sixth player adds a red counter, and the pile ends at the tally 4-3.

This means there are more red counters at the end of the game.

Notice that only the parity (evenness or oddness) of the tally numbers matter, and so we can see that the state after the second player's turn is the same as the state after the fifth player's turn, except with 2 extra counters of each color.

This means that with more players, the game would cycle forever with the pattern green-red-both-green-red-both added by players from the second onwards. If we pick a number of players that is one less than a multiple of 3 (2, 5, 8, ...) then there will be an equal number of red and green counters, and otherwise there will be one more red counter than green.

10. This quiz has the same number of "red" answers as "green". What, then, is the answer to this question?

Answer: Red

If there are the same number of "red" answers as "green", then there are half of each color i.e. five "red" answers and five "green".

So far, we have had four "red" answers and five "green", so we need a final "red" answer to achieve equality.

Source: Author AdamM7

This quiz was reviewed by FunTrivia editor spanishliz before going online.
Any errors found in FunTrivia content are routinely corrected through our feedback system.

Red and Green Trivia Quiz

A diverse set of logic puzzles with the possible answers "red" and "green".

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