Riddles and Brain Teasers

A completely black dog was strolling down main street during a total blackout affecting the entire town. Not a single streetlight had been on for hours. As the dog crosses the center of the road a Buick Skylark with two broken headlights speeds towards it, but manages to swerve out of the way just in time. How could the driver see the dog to swerve in time?

Show the answer »

It was during the day.

Posted in Brain Teasers

False Positive HIV Test

Imagine an HIV test that is 95% accurate (false positive rate of 5%) and around 2% of the tested population is infected with HIV. What is the probability that you actually have HIV when your test comes back positive?

Show the answer »

29%

To read more about this, see the False Positive Paradox page on Wikipedia.

Posted in Brain Teasers

Ten Times Two is 0218

10 × 2 = 0218
20 × 2 = 1421
30 × 2 = 1632
40 × 2 = ?

Show the answer »

2840.This makes the first column the start of the Fibonacci series: 0, 1, 1, 2.
The second column is the even numbers: 2, 4, 6, 8
The third column is counting up by ones: 1, 2, 3, 4
And the last column is the answer in the first row in reverse: 8, 1, 2, 0.Don’t ask what 50 × 2 equals. I have no idea. :)Thanks to Jim for helping with the solution.

2840.

This makes the first column the start of the Fibonacci series: 0, 1, 1, 2.
The second column is the even numbers: 2, 4, 6, 8
The third column is counting up by ones: 1, 2, 3, 4
And the last column is the answer in the first row in reverse: 8, 1, 2, 0.

Don’t ask what 50 × 2 equals. I have no idea. :)

Thanks to Jim for helping with the solution.

Posted in Brain Teasers

Tagged with Series

Four Against the Masses

We are four against the masses. We are trying to find the one who is the whole package. We sigh, we laugh, we frown while we hope that the next one will be the one. Who are we?

Show the answer »

Four orphaned siblings. It seems like there may be a better answer than this. If you have one, please add a comment.

Posted in Riddles

All Things Devours

This thing all things devours,
Birds, beasts, trees, and flowers.
Gnaws iron bites steel,
Grinds hard stones to meal,
Slays king, ruins town,
And beats high mountain down

Show the answer »

Time. Iron, steel, stone and virtually any substance will be worn down given enough time.

(From J.R.R. Tolkien’s The Hobbit)

Posted in Riddles

yyyy UR

yyyy U R, yyyy U B, I C U R y y 4 ?

What word belongs in place of the question mark?

Show the answer »

Me.
Wise you are, wise you be, I see you are too wise for me.

Posted in Riddles

More ›