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
10 From 100 Riddle
Hint:
The Coin Toss Riddle
You are in a bar having a drink with an old friend when he proposes a wager.
"Want to play a game?" he asks.
"Sure, why not?" you reply.
"Ok, here's how it works. You choose three possible outcomes of a coin toss, either HHH, TTT, HHT or whatever. I will do likewise. I will then start flipping the coin continuously until either one of our combinations comes up. The person whose combination comes up first is the winner. And to prove I'm not the cheating little weasel you're always making me out to be, I'll even let you go first so you have more combinations to choose from. So how about it? Is $10.00 a fair bet?"
You know that your friend is a skilled trickster and usually has a trick or two up his sleeve but maybe he's being honest this time. Maybe this is a fair bet. While you try and think of which combination is most likely to come up first, you suddenly hit upon a strategy which will be immensely beneficial to you. What is it?
"Want to play a game?" he asks.
"Sure, why not?" you reply.
"Ok, here's how it works. You choose three possible outcomes of a coin toss, either HHH, TTT, HHT or whatever. I will do likewise. I will then start flipping the coin continuously until either one of our combinations comes up. The person whose combination comes up first is the winner. And to prove I'm not the cheating little weasel you're always making me out to be, I'll even let you go first so you have more combinations to choose from. So how about it? Is $10.00 a fair bet?"
You know that your friend is a skilled trickster and usually has a trick or two up his sleeve but maybe he's being honest this time. Maybe this is a fair bet. While you try and think of which combination is most likely to come up first, you suddenly hit upon a strategy which will be immensely beneficial to you. What is it?
Hint: Think what would be most likely to happen if you chose HHH, would this be a good decision?
The answer is to let your friend go first. This puzzle is based on an old game/scam called Penny Ante. No matter what you picked, your friend would be able to come up with a combination which would be more likely to beat yours. For example, if you were to choose HHH, then unless HHH was the first combination to come up you would eventually lose since as soon as a Tails came up, the combination THH would inevitably come up before HHH. The basic formula you can use for working out which combination you should choose is as follows. Simply take his combination (eg. HHT) take the last term in his combination, put it at the front (in this case making THH) and your combination will be more likely to come up first. Try it on your friends! Did you answer this riddle correctly?
YES NO
YES NO
Die Toss Riddle
If you toss a die and it comes up with the number one 9 times in a row, what is the probability that it will come up with one on the next throw?
Hint:
Bringing Back The Lost
It brings back the lost as though never gone, shines laughter and tears with light long since shone,
a moment to make, a life time to shed, valued then but lost when your dead. What is it?
a moment to make, a life time to shed, valued then but lost when your dead. What is it?
Hint:
A Fathers Murder
A man goes to his mother funeral, there, he meets a woman. They go out and the part there separate ways. The man forgets to get the woman's phone number. Three days later he kills his Father...Why?
Hint:
So the woman would go to his father's funeral and he can get her number this time....98% of people who got this right turned out to be serial killers... Did you answer this riddle correctly?
YES NO
YES NO
On Display In December
I have numbers on me but Im not a phone
I have several doors but Im not a car
Im on display in December but Im not a nativity scene
Im not seen after Christmas Day but Im not a cookie for Santa
I often contain chocolate but Im not an Easter egg
What am I?
I have several doors but Im not a car
Im on display in December but Im not a nativity scene
Im not seen after Christmas Day but Im not a cookie for Santa
I often contain chocolate but Im not an Easter egg
What am I?
Hint:
Calling Santa Riddle
Hint:
In Your Spine
Your body has lots of these
Including the tibia
Several are in your spine
And theres three in your ear
What are they?
Including the tibia
Several are in your spine
And theres three in your ear
What are they?
Hint:
A 10 Foot Rope Ladder
A 10 foot rope ladder hangs over the side of a boat with the bottom rung on the surface of the water. The rungs are one foot apart, and the tide goes up at the rate of 6 inches per hour. How long will it be until three rungs are covered?
Hint:
Only Made Of Bones
This body has no ears or tongue
So hes not able to use phones
Tickling doesnt work on him
Because hes only made of bones
Who is this guy?
So hes not able to use phones
Tickling doesnt work on him
Because hes only made of bones
Who is this guy?
Hint:
Old Man On London Bridge
I met an old man on London bridge,
As the sun set on the ridge,
He tipped his hat and drew his name,
And cheated at the guessing game.
What was the mans name?
As the sun set on the ridge,
He tipped his hat and drew his name,
And cheated at the guessing game.
What was the mans name?
Hint:
Andrew. In the third line, and drew his name. It works better when you say it. Did you answer this riddle correctly?
YES NO
YES NO
Taking You To School
This vehicle makes frequent stops
So getting to places can be slow
In London theyre usually red
The ones you take to school are yellow
So getting to places can be slow
In London theyre usually red
The ones you take to school are yellow
Hint:
Bus Driver Riddle
Ok, you're the bus driver, there were 20 kids on the bus. At the first stop, 2 kids get on but 5 kids get off. The second stop, 3 kids get off but 1 gets on. The third stop, 8 kids get off but only 3 kids get off. Who's the bus driver?
Hint:
Two Brothers Riddle
Two brothers we are, great burdens we bear,
All day we are bitterly pressed;
Yet this we will say, we are full all the day
And empty when we go to rest.
What are we?
All day we are bitterly pressed;
Yet this we will say, we are full all the day
And empty when we go to rest.
What are we?
Hint: Your burdens are also our burdens, but greater by the measure of you.
Add Your Riddle Here
Have some tricky riddles of your own? Leave them below for our users to try and solve.