What is the Chance That You’ll Be Correct?

If you choose an answer to this question at random, what is the chance that you will be correct?

a) 25%
b) 50%
c) 60%
d) 25%

This is becomes a self-referential paradox. Both A and D would be correct if there were four unique answers, but since A and D are the same answer, the chance that you would choose a correct answer is 50%, which makes B correct. But if there’s only one correct answer, the odds of choosing the correct one at random goes back to 25%. And around and round you go.

There’s a lot of discussion at Richard Wiseman’s blog and more at Lifehacker, where I first saw this.

Posted in Brain Teasers

The Bus Driver

You are the bus driver. At your first stop, you pick up 29 people. On your second stop, 18 of those 29 people get off, and at the same time 10 new passengers arrive. At your next stop, 3 of those 10 passengers get off, and 13 new passengers come on. On your fourth stop 4 of the remaining 10 passengers get off, 6 of those new 13 passengers get off as well, then 17 new passengers get on. What is the color of the bus driver’s eyes?

The eye color of the reader of this problem. The first sentence is the key: “You are the bus driver”.

Posted in Brain Teasers

I Move Quickly

Physicists have built devices to make me move quickly. My last eight letters can be commonly found in newspapers, magazines, and journals.

What am I?

Particles. Physicists use particle accelerators and newspapers, magazines and journals have articles.

Posted in Riddles
Tagged with

Bricks to Finish a Building

How many bricks does it take to finish a brick building?

One (the last one is the only one that can finish the building).

Posted in Riddles

How Much Time is Left in the Exam?

During a math exam, Willy asks Ms. Matilda, the teacher, how much time is left. Ms. Matilda is known for being obtuse and answers that the amount of time left is 1/5 of the time already completed and that is also how much time is left, in a manner of speaking.

How much time is left?

15 minutes. The total exam time is 90 minutes. If 15 minutes are left, 75 minutes have already passed, and one fifth of 75 is 15. However, if you follow Ms. Matilda’s hint and pay attention to only the numbers in 1/5, you get the answer of 15 minutes as well.

Posted in Brain Teasers

A Metal Roof and a Glass Wall

I have a metal roof and a glass wall,
I burn and burn but never fall.

What am I?

A lantern.

Posted in Riddles
Tagged with

Never Was, Always To Be

I never was, am always to be. No one ever saw me, nor ever will. And yet I am the confidence of all, To live and breathe on this terrestrial ball. What am I?

Tomorrow or the future.

Posted in Riddles

If I Didn’t Exist, You Wouldn’t Either

I’m a six-letter word. If I did not exist, you wouldn’t either. With my first letter omitted I’m an alternative. The last three letters are feminine. The first four letters make an insect.

Who am I?

Mother

other = an alternative
her = feminine
moth = an insect

Posted in Riddles

Two Faces But Show You One

I have two faces, but show you one.
I once had guests, but now have none.
I’m rarely bloody and seldom blue.
I’m often promised and sometimes new.

The moon. It has two sides, but on earth we only ever see one side. Man has been on the moon, but no one is there now. A full lunar eclipse is known as a blood moon, and the phrase “once in a blue moon” refers to something that rarely happens. Promising the moon is making an extravagant or impossible promise, and there’s a new moon once every lunar cycle.

Posted in Riddles
Tagged with

The Odd One Out

Which is the odd one out and why?

A. Cassius
B. Cassia
C. Casca

B. Cassia is a tropical tree; Cassius and Casca were conspirators against Julius Caesar.

Posted in Brain Teasers