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

Your Father’s Sister’s Sister-in-law

What relation would your father’s only single sister’s sister-in-law be to you?

Your mother.

Posted in Brain Teasers

A Red Robe and Staff In Hand

I wear a red robe,
With staff in hand,
And a stone in my throat.
Cut me and I weep red tears

What am I?

A cherry

There are a few other variations of this one:

As I went through the garden gap,
Who should I meet but Dick Red-cap!
A stick in his hand, a stone in his throat,
If you’ll tell me this riddle, I’ll give you a groat.
(Said to be the lyrics to A Cherry)

I slipped down a slippery gap,
Found a man with a red cap,
He had a stick in his back and a stone in his belly,
Riddle me this and I’ll give you a penny.

Posted in Riddles

A Word That Has No End

I’m a five-letter word that has no end, Commit a sin? One through three can amend, One, four and five are something alive, Two and three occur near to thee.

What am I?

Abyss. aby is an archaic word meaning to pay the penalty for. An ass, otherwise known as a donkey, is alive and “by” is another way of saying near to you.

Posted in Riddles

I Wear You Down

I wear you down, yet you will mourn me once I fly.
You can kill me, but I will never die.

Time.

(found in The Copper Gauntlet by Holly Black and Cassandra Clare)

Posted in Riddles

The Right Combination of Letters and Values

The letters A through H can be assigned the following values to make all the equations true. Find the right combination of letter values.

Values: 1, 4, 5, 7, 9, 14, 16, 21

C + F = G
A + C = F
B + G = D
B + E = H
D + F = H

A = 1
B = 7
C = 4
D = 16
E = 14
F = 5
G = 9
H = 21

Posted in Brain Teasers

Sisters and Brothers

My daughter has as many sisters as she has brothers. Each of her brothers has twice as many sisters as brothers. How many sons and daughters do I have?

Four daughters and three sons. Each daughter has 3 sisters and 3 brothers, and each brother has 2 brothers and 4 sisters.

To figure it out mathematically, you could use the following two equations where G = the number of girls and B = the number of boys:
G – 1 = B
2(B – 1) = G

Solving for G gives you 4 and plugging that in to G – 1 = B gives you a B of 3.

Posted in Brain Teasers

Rhonda At the Ballet

Rhonda will go see ballet but not the opera. Her favorite number is eight and she doesn’t like nine. She likes salmon but not trout. She hates Mondays and likes Wednesdays. Does she use a comb or a brush?

A comb. Rhonda likes words with silent letters, like her name.

Posted in Brain Teasers

Travel Far Before You Turn It Over

You have to travel far before you turn it over. What is it?

An odometer.

Posted in Riddles

ABCD equals DCBA

What 4-digit number abcd satisfies this equation?

4 × abcd = dcba

2178

4 × 2178 = 8712

Posted in Brain Teasers