The 100 Seat Airplane
People are waiting in line to board a 100-seat airplane. Steve is the first person in the line. He gets on the plane but suddenly can't remember what his seat number is, so he picks a seat at random. After that, each person who gets on the plane sits in their assigned seat if it's available, otherwise they will choose an open seat at random to sit in.
The flight is full and you are last in line. What is the probability that you get to sit in your assigned seat?
The flight is full and you are last in line. What is the probability that you get to sit in your assigned seat?
Hint: You don't need to use complex math to solve this riddle. Consider these two questions:
What happens if somebody sits in your seat?
What happens if somebody sits in Steve's assigned seat?
The correct answer is 1/2.
The chase that the first person in line takes your seat is equal to the chance that he takes his own seat. If he takes his own seat initially then you have a 100% chance of sitting in your seat, if he takes your seat you have a 0 percent chance. Now after the first person has picked a seat, the second person will enter the plan and, if the first person has sat in his seat, he will pick randomly, and again, the chance that he picks your seat is equal to the chance he picks someone your seat. The motion will continue until someone sits in the first persons seat, at this point the remaining people standing in line which each be able to sit in their own seats. Well how does that probability look in equation form? (2/100) * 50% + (98/100) * ( (2/98) * 50% + (96/98) * ( (2/96) * (50%) +... (2/2) * (50%) ) ) This expansion reduces to 1/2.
An easy way to see this is trying the problem with a 3 or 4 person scenario (pretend its a car). Both scenarios have probabilities of 1/2. Did you answer this riddle correctly?
YES NO
The chase that the first person in line takes your seat is equal to the chance that he takes his own seat. If he takes his own seat initially then you have a 100% chance of sitting in your seat, if he takes your seat you have a 0 percent chance. Now after the first person has picked a seat, the second person will enter the plan and, if the first person has sat in his seat, he will pick randomly, and again, the chance that he picks your seat is equal to the chance he picks someone your seat. The motion will continue until someone sits in the first persons seat, at this point the remaining people standing in line which each be able to sit in their own seats. Well how does that probability look in equation form? (2/100) * 50% + (98/100) * ( (2/98) * 50% + (96/98) * ( (2/96) * (50%) +... (2/2) * (50%) ) ) This expansion reduces to 1/2.
An easy way to see this is trying the problem with a 3 or 4 person scenario (pretend its a car). Both scenarios have probabilities of 1/2. Did you answer this riddle correctly?
YES NO
Footprints Between Two Parallel Lines Riddle
Hint:
Add Up To 100 Riddle
With the numbers 123456789, make them add up to 100. They must stay in the same order. You can use addition, subtraction, multiplication, and division. Remember, they have to stay in the same order!
Hint:
A Bed That Never Sleeps
Hint:
What Has A Foot But No Legs Riddle
Hint:
100 Widgets Riddle
Hint:
It would take 5 minutes. Each machine takes 5 minutes to make its widget. Therefore, each of the 100 machines would have finished making its widget in 5 minutes. Did you answer this riddle correctly?
YES NO
YES NO
The Foot Of A Wolf Riddle
Hint:
100 Meter Sprint Riddle
Hint:
100 Lawyers Riddle
Hint:
Less Than 100 Riddle
Find a number less than 100 that is increased by one-fifth of its value when its digits are reversed.
Hint:
Little Johnny's Bet Riddle
Little Johnny is walking home. He has $300 he has to bring home to his mom. While he is walking a man stops him and gives him a chance to double his money. The man says "I'll give you $600 if you can roll 1 die and get a 4 or above, you can roll 2 dice and get a 5 or 6 on at least one of them, or you can roll 3 dice and get a 6 on at least on die. If you don't I get your $300."
What does Johnny do to have the best chance of getting home with the money?
What does Johnny do to have the best chance of getting home with the money?
Hint:
He just doesn't take the bet. This gives him a 100 percent chance of getting the money home. If he takes the bet with 1 die he has a 50 percent chance of winning. If he takes the bet with 2 dice he has about a 56 percent chance of winning. If he takes the bet with 3 dice he has about a 42 percent chance of winning. Did you answer this riddle correctly?
YES NO
YES NO
Little Johnny's Cats Riddle
Little Johnny's teacher asks him, "If I gave you two cats, then two more, and two more cats; how many would you have?"
Little Johnny replies, "Seven!"
His teacher asks him again more slowly, "If I gave you two cats, then two more, and two more cats; how many would you have?"
But again Little Johnny replies, "Seven!"
Next she asks, "If I get two cats, then two more, and two more cats; how many would I have?"
Little Johnny replies, "Six!"
"Good Job Johnny! Now if I gave you two cats, then two more, and two more cats; how many would you have?"
Johnny thinks for a second, "Seven."
But Johnny is not wrong. Why?
Little Johnny replies, "Seven!"
His teacher asks him again more slowly, "If I gave you two cats, then two more, and two more cats; how many would you have?"
But again Little Johnny replies, "Seven!"
Next she asks, "If I get two cats, then two more, and two more cats; how many would I have?"
Little Johnny replies, "Six!"
"Good Job Johnny! Now if I gave you two cats, then two more, and two more cats; how many would you have?"
Johnny thinks for a second, "Seven."
But Johnny is not wrong. Why?
Hint:
John's Three Daughters Riddle
John has three daughters who are all unmarried. The youngest always lies, the oldest always tells the truth, and the one in the middle either tells the truth or lies. A very rich young man comes to John's house and says he wishes to marry one of his daughters. Naturally he wants to marry the oldest or the youngest so he will always know if she is lying or telling the truth. John agrees but says he can only ask one of the girls a yes or no question to decide which one he marries. They all look the same age.
What one question does he ask one of the daughters at random to figure out which daughter is the youngest or oldest?
What one question does he ask one of the daughters at random to figure out which daughter is the youngest or oldest?
Hint:
"Is she older than her?"
Explanation: (He would ask one of the daughters if one of the other daughters is older than the last daughter). He always should pick the younger daughter based on what he knows. If he asks the older daughter and she says yes, then the youngest daughter will be known. If he asks the older daughter and she says no, then the youngest daughter is the other one. If he asks the youngest daughter and she says yes, she is lying and he will still pick the oldest. If he asks the youngest and she says no, he will just pick the other like in the first case. If he asks the middle daughter it doesn't matter because both will be acceptable choices. Did you answer this riddle correctly?
YES NO
Explanation: (He would ask one of the daughters if one of the other daughters is older than the last daughter). He always should pick the younger daughter based on what he knows. If he asks the older daughter and she says yes, then the youngest daughter will be known. If he asks the older daughter and she says no, then the youngest daughter is the other one. If he asks the youngest daughter and she says yes, she is lying and he will still pick the oldest. If he asks the youngest and she says no, he will just pick the other like in the first case. If he asks the middle daughter it doesn't matter because both will be acceptable choices. Did you answer this riddle correctly?
YES NO
100 Billion Neurons Riddle
Hint:
The 100th Floor Riddle
A man lives on the 100th floor of his apartment building. Every day he takes the elevator down from his apartment to the lobby. After work, he takes the elevator from the lobby to the 50th floor and walks up the stairs the rest of the way. On rainy days he takes the elevator all the way from the lobby to the 100th floor. Why?
Hint:
The man was a dwarf. On rainy days he had an umbrella to help him press the button 100. Did you answer this riddle correctly?
YES NO
YES NO
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