esroh gnidir

What does this represent?

esroh gnidir

Horse back riding. The words are horse and riding spelled backwards.

Posted in Brain Teasers

Bank Wait Times

Suppose a small bank has one teller and customer transactions take 10 minutes on average. With 5.8 customers arriving per hour, what is the expected wait time? What would it be if you added a second teller?

With one teller, customers will wait nearly five hours on average. But adding a second teller makes the wait go down to 3 minutes.

Thanks to John D. Cook for this one.

Posted in Brain Teasers

Two Eights and Two Threes to Make Twenty Four

Using one or more addition, subtraction, multiplication or division operations, what formula using the numbers 3, 3, 8 and 8 equals 24?

8 ÷ (3 – (8 ÷ 3)) = 24

Posted in Brain Teasers

Scrambled Auctioned

What are two other words (anagrams) that can be made from the letters in “auctioned”?

1. Cautioned
2. Education

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Leaves That Don’t Fall

I have wood but no bark,
And leaves that don’t fall,
I am made up of branches,
and come in sizes of all.

I am completely devoured many times,
over and over by a worm of a kind.
If you want to know the answer of mine,
look for the secret that I’ve stored inside.

What am I?

A library or bookstore.

Posted in Riddles
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Only Useful When Full

I am only useful when I’m full,
Yet I am always full of holes.

What am I?

A sieve, used for straining food like pasta.

Posted in Riddles

Highest Product Using All Digits

What is the highest product that can be generated by multiplying two numbers while only using each digit once (1 through 9)?
For example, 12345678 * 9 = 111,111,102

9642 * 87531 = 843,973,902

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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 Japanese IQ Test

Supposedly this is given as a test in Japan. I have no idea if that’s accurate.

There are 8 people who have to cross the river on a raft.

1. Policeman
2. Thief
3. Father
4. Boy 1
5. Boy 2
6. Mother
7. Girl 1
8. Girl 2

The rules are:

Only two people can cross at a time.
Only the adults can operate the raft.
The father can’t be with the girls unless the mother is there.
The mother can’t be with the boys unless the father is there.
The thief can’t remain with anyone unless the policeman is present.

How do you get them all across?

Instead of working it out by hand, here’s a flash version.

Click on the circle to start. Click on a person to put them on the raft and click on the lever to make the raft cross.

Here’s how I did it in 17 steps. Can you do it faster? Let me know in the comments.

1. Policeman (P)
2. Thief (T)
3. Father (F)
4. Boy 1 (B1)
5. Boy 2 (B2)
6. Mother (M)
7. Girl 1 (G1)
8. Girl 2 (G2)

1. P, T →
2. ← P

3. P, B1 →
4. ← P T

5. F, B2 →
6. ← F

7. F, M →
8. ← M

9. P, T →
10. ← F

11. M, F →
12. ← M

13. M, G1 →
14. ← P T

15. P, G2 →
16. ← P

17. P, T →

Posted in Brain Teasers

At Least One is a Boy

A couple has two children. At least one of them is a boy. Assuming the probability of having a boy or girl is 50%, what is the probability that both children are boys?

If you answered 1/2, you’re not without comrades, but the generally accepted answer by statisticians (though not without debate) is 1/3. This is because there are four possible combinations: boy-boy, boy-girl, girl-boy and girl-girl. Since we are told one of the children is a boy (but we don’t know if it’s the first or second child), we can rule out the girl-girl combination, leaving three remaining options. Only one out of 3 is boy-boy, so we get a 1/3 chance.

This is a well-known problem known as the Boy or Girl paradox. The other variation is this brain teaser.

Posted in Brain Teasers