The Prime Number Riddle
Two hundred people in an auditorium are asked to think of a single digit number from 1 to 9 inclusive and write it down. All those who wrote down a prime number are now asked to leave. Ninety people remain behind in the hall. How many of these are expected to have written down an odd number?
Hint: Remember that 1 is not a prime number.
Those that remain behind must have written {1,4,6,8,9} and from this only {1,9} are odd. The probability of an odd number is thus 2/5.
Expected number of odds is 2/5 * 90 = 36 Did you answer this riddle correctly?
YES NO
Expected number of odds is 2/5 * 90 = 36 Did you answer this riddle correctly?
YES NO
I Am Up In The Sky
Hint:
Ears That Cannot Hear
This is a common riddle that's very simple but can be tricky if you don't catch the clues provided in the question. Can you solve this riddle in under 30 seconds?
Hint: The ears aren't human ears.
Halfway To 100
Hint:
Seven Dimes And A Nickel Riddle
Hint:
Between 70 And 90 Riddle
Hint:
More Than 80 Riddle
Hint:
My Digits Are 5 And 9 Riddle
Hint:
Dead President Riddle
Hint:
Pink Car Riddle
Hint:
Smell Very Sweet Riddle
I am a melon that is orange on the inside with lots of seeds. I smell very sweet. My vitamin A helps to give you strong bones. What am I?
Hint:
Locks That Don't Need A Key
I had many locks that don't need a key
I was far too many for you to count me
I was never to be shortened, for a vow had been said
I was a symbol of strength that flowed from the head
But in a moment of weakness, my secret was out
I lay all in pieces when she gave the shout
I'm in the Bible - what am I?
I was far too many for you to count me
I was never to be shortened, for a vow had been said
I was a symbol of strength that flowed from the head
But in a moment of weakness, my secret was out
I lay all in pieces when she gave the shout
I'm in the Bible - what am I?
Hint: Judges 16
Ghost Rooms Riddle
Hint:
A Transport You Don't Drive
I'm a transport you don't have to drive
Which means you can sit back and relax
I can take you across the country
Not in the air but along some tracks.
What could I be?
Which means you can sit back and relax
I can take you across the country
Not in the air but along some tracks.
What could I be?
Hint:
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
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