The Secret Santa Exchange
A group of ten friends decide to exchange gifts as secret Santas. Each person writes his or her name on a piece of paper and puts it in a hat. Then each person randomly draws a name from the hat to determine who has him as his or her secret Santa. The secret Santa then makes a gift for the person whose name he drew.
When it's time to exchange presents, each person walks over to the person he made the gift for and holds his or her left hand in his right hand.
What is the probability that the 10 friends holding hands form a single continuous circle?
When it's time to exchange presents, each person walks over to the person he made the gift for and holds his or her left hand in his right hand.
What is the probability that the 10 friends holding hands form a single continuous circle?
Hint: It's not as difficult as it seems.
It's the number of ways the friends can form a circle divided by the number of ways the names can be drawn out of the hat.
1/10
For a group of n friends, there are n! (n factorial) ways to draw the names out of the hat. Since a circle does not have a beginning and end, choose one person as the beginning and end of the circle. There are now (n-1)! ways to distribute the remaining people around the circle. Thus the probability of forming a single circle is
(n-1)! / n!
Since n! = (n-1)! * n (for n > 1), this can be rewritten as
(n-1)! / (n*(n-1)!)
Factoring out the (n-1)! from the numerator and denominator leaves
1/n
as the probability. Did you answer this riddle correctly?
YES NO
For a group of n friends, there are n! (n factorial) ways to draw the names out of the hat. Since a circle does not have a beginning and end, choose one person as the beginning and end of the circle. There are now (n-1)! ways to distribute the remaining people around the circle. Thus the probability of forming a single circle is
(n-1)! / n!
Since n! = (n-1)! * n (for n > 1), this can be rewritten as
(n-1)! / (n*(n-1)!)
Factoring out the (n-1)! from the numerator and denominator leaves
1/n
as the probability. Did you answer this riddle correctly?
YES NO
The Cheap Mp3 Player
My MP3 player is cheap 'n' nasty and has now broken: it is stuck on 'Shuffle'. In this mode it starts with whatever track you put it on, but then plays tracks in a random order. The only restriction is it never plays a song that's already been played that day.
I purchased my favourite murder mystery book in audio format, and put the first 6 chapters on my MP3 player. (Each chapter is exactly 1 track.) There's nothing else on my player at the moment. What is the probability that I will hear the 6 chapters in order as I listen today, without having to change tracks at all? (Obviously, I will ensure it plays chapter 1 first.)
The next day I empty the player before putting on the next 6 chapters. This time I also transfer a CD of mine with 11 songs on. I don't mind songs coming in between the chapters of my book, as long as the chapters are in order. What's the probability of that happening now?
I purchased my favourite murder mystery book in audio format, and put the first 6 chapters on my MP3 player. (Each chapter is exactly 1 track.) There's nothing else on my player at the moment. What is the probability that I will hear the 6 chapters in order as I listen today, without having to change tracks at all? (Obviously, I will ensure it plays chapter 1 first.)
The next day I empty the player before putting on the next 6 chapters. This time I also transfer a CD of mine with 11 songs on. I don't mind songs coming in between the chapters of my book, as long as the chapters are in order. What's the probability of that happening now?
Hint:
With only 6 tracks on the player:
The first chapter has been set to play first. The probability of the next 5 chapters playing in order is 1/5! = 1/120.
With the music on the player as well:
Seeing as I don't care about when the music plays, it doesn't change anything. The answer is still 1/120. Did you answer this riddle correctly?
YES NO
The first chapter has been set to play first. The probability of the next 5 chapters playing in order is 1/5! = 1/120.
With the music on the player as well:
Seeing as I don't care about when the music plays, it doesn't change anything. The answer is still 1/120. Did you answer this riddle correctly?
YES NO
Santas Suit Riddle
Hint:
Ligaments Connect Riddle
You will find 206
Inside adult human bodies
Together theyre a skeleton
Ligaments connect all of these
They are?
Inside adult human bodies
Together theyre a skeleton
Ligaments connect all of these
They are?
Hint:
When You Are Sad Riddle
When you are sad
You tear out my insides
When I am finished
You crush my outsides
You choose my insides
Whatever feels good
Picking out my outsides
Thinking about yourself
What am I?
You tear out my insides
When I am finished
You crush my outsides
You choose my insides
Whatever feels good
Picking out my outsides
Thinking about yourself
What am I?
Hint:
A tissue box
When you are crying, you use a tissue to wipe your tears
When all of the tissues are gone, you crush the box, and recycle it
Usually you would like a nice tissue, not a scratchy one
The outside of a tissue box can explain your personality Did you answer this riddle correctly?
YES NO
When you are crying, you use a tissue to wipe your tears
When all of the tissues are gone, you crush the box, and recycle it
Usually you would like a nice tissue, not a scratchy one
The outside of a tissue box can explain your personality Did you answer this riddle correctly?
YES NO
Money In The Freezer Riddle
Hint:
Trapped With The Army
A man got trapped with the army, there were two papers, one said yes the other no. A man in the army said if you get the paper that sees no I will kill you, another man comes in the room sees I put no on both papers. How does he get out of it?
Hint:
He eats one. The man looks at the paper it sees no, so he thought the one the guy ate was yes. Did you answer this riddle correctly?
YES NO
YES NO
Fireplace Bed Riddle
Hint:
A Sharpshooter Riddle
A sharpshooter hangs up his hat, turns around and walks 5000 meters, then turns around and shoots his gun, putting a hole right through his hat. How did he do it?
Hint:
Eat, Cook, Throwaway
You throw away the outside and cook the inside and then you eat the outside and throw the inside. What is it?
Hint:
Comes In Any Size
Hint:
Sometimes Made Into A Coin
Im sometimes made into a coin
And sometimes into an ingot
When at the end of a rainbow
I am what is inside the pot
What am I?
And sometimes into an ingot
When at the end of a rainbow
I am what is inside the pot
What am I?
Hint:
Strive With Wind And Wave Riddle
Off I must strive with wind and wave, battle them both
when under the sea.
I feel out the bottom, a foreign land. In lying still, I am
Strong in the strife;
If I fail in that, they are stronger than I, and
Wrenching me loose, soon put me to rout.
They wish to capture what I must keep. I can master
Them both if my grip holds out,
If the rocks bring succor and lend support, strength
In the struggle. Ask my name
when under the sea.
I feel out the bottom, a foreign land. In lying still, I am
Strong in the strife;
If I fail in that, they are stronger than I, and
Wrenching me loose, soon put me to rout.
They wish to capture what I must keep. I can master
Them both if my grip holds out,
If the rocks bring succor and lend support, strength
In the struggle. Ask my name
Hint:
I Am A Kind Of Coat
Hint:
One Light And Three Switches
This riddle is a favorite among many. No diversions into logical theory or mathematics, just a fun puzzle with a satisfying answer.
How do you figure out without a doubt which switch controls the light?
Hint:
Flip switch number 1 and wait a few minutes. Flip switch number 1 back to its original position, and then immediately flip switch number 2.
Open the door. If the light is on, then switch number 2 controls it. If the light is off, then go and feel the bulb with your hand. If the bulb is hot, the switch number 1 controls it, and if the bulb is cold, then switch number 3, the one you did not touch, controls it. Did you answer this riddle correctly?
YES NO
Open the door. If the light is on, then switch number 2 controls it. If the light is off, then go and feel the bulb with your hand. If the bulb is hot, the switch number 1 controls it, and if the bulb is cold, then switch number 3, the one you did not touch, controls it. Did you answer this riddle correctly?
YES NO
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