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?

29%

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

Posted in Brain Teasers

Mother From a Family of Eight

This mother comes from a family of eight,
Supports her children in spite of their weight,
Turns around without being called,
Has held you since the time you crawled.

Who is she?

“Mother” Earth. The family of eight are the eight planets, all of the world’s population is quite a load, the earth is always spinning (or turning around) and unless you’re an alien, you’ve been on earth your whole life.

Posted in Riddles

Money Is Right Above My Reach

Money is right above my reach, I’m barely staying out of The Emergency Room (It is right below me), Room #3 is to my left, Room #5 is to my right with a 5% interest rate.

What am I?

The number 4 key on a QWERTY keyboard. $ is money, ER (an abbreviation for Emergency Room) are the two letters immediately below the number 4 key, the #/3 key is to the left and the 5/% key is to the right.

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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

Three Burning Rooms

Three rooms contain:
1) Gold coins
2) Currency notes
3) Cotton bags

If all three rooms catch fire, which room will the ambulance pour water on first?

An ambulance doesn’t pour water.

Posted in Brain Teasers

Sharing Apples

How do you share 15 apples evenly with 16 people?

Make applesauce.

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Cut One Off And I Become Stronger

I have three letters. Cut one off and I become stronger. Cut two off and I become ten. What am I?

A fox. Removing the f leaves ox, a strong animal. Cutting off the fo leaves X, the roman numeral for 10.

Posted in Riddles
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Groups of Creatures

These are names given to groups of creatures or things, but they have been scrambled. What is the correct arrangement?

Colony of Birds
Horde of Spiders
Den of Wild Pigs
Clutter of Crows
Nest of Snakes
Park of Elks
Doylt of Ferrets
Gang of Machine Guns
Business of Swine
Volery of Artillery
Hover of Gnats
Drift of Frogs

Colony of Frogs
Horde of Gnats
Den of Snakes
Clutter of Spiders
Nest of Machine Guns
Park of Artillery
Doylt of Swine
Gang of Elks
Business of Ferrets
Volery of Birds
Hover of Crows
Drift of Wild Pigs

Posted in Brain Teasers

A Seemingly Simple Math Problem

What is the answer to this problem?

1 + 1 + 1 + 1 + 1
1 + 1 + 1 + 1 + 1
1 + 1 × 0 + 1 = ?

30.

There are two tricks to this one. The first is 1 × 0. But it’s mostly there as a distraction. Yes, 1 × 0 is 0, but that doesn’t affect anything else in the equation. The second, far trickier element is that the lines ending with 1 don’t have a + sign next to them. That means they should be combined with the following line.

Let’s put the equation all on one line, shall we?

1 + 1 + 1 + 1 + 11 + 1 + 1 + 1 + 11 + 1 × 0 + 1 = ?

And the answer to that equation is 30.

Posted in Brain Teasers

Shave Everyday

I can shave everyday but my beard will stay. Who am I?

A barber.

Posted in Riddles