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

Hidden Gems

Find the names of 10 gems or precious stones hidden in the following story. Each one spans at least two words.

Sir Gade rode toward a castle atop a zebra at a steady gallop, a long way from home. He arrived at the gate and the keeper knelt in shame. “Thy steed must be tired.” Sir Gade replied, “I am on direct orders from the King. Let me through.” A cougar, nettled by the noise, emerged from a shrub. “You must save me!” cried the gate man. Sir Gade, eyes filled with rancor, alighted and gazed toward the sky. An item fell from his cloak as drove his sword into the cougar’s spine. “Let me pass!” cried Sir Gade. The gate keeper, stunned from his saga, tentatively opened the gate, then retrieved the fallen item.

1. topaz – “atop a zebra”
2. opal – “gallop, a long”
3. amethyst – “shame. Thy steed”
4. diamond – “replied, I am on direct”
5. garnet – “cougar, nettled”
6. ruby – “shrub. You”
7. coral – “rancor, alighted”
8. kyanite – “sky. An item”
9. spinel – “spine. Let”
10. agate – “saga, tentatively”

Sir Gade rode toward a castle atop a zebra at a steady gallop, a long way from home. He arrived at the gate and the keeper knelt in shame. “Thy steed must be tired.” Sir Gade replied, “I am on direct orders from the King. Let me through.” A cougar, nettled by the noise, emerged from a shrub. “You must save me!” cried the gate man. Sir Gade, eyes filled with rancor, alighted and gazed toward the sky. An item fell from his cloak as drove his sword into the cougar’s spine. “Let me pass!” cried Sir Gade. The gate keeper, stunned from his saga, tentatively opened the gate, then retrieved the fallen item.

Posted in Riddles

Humans and Animals

I am important to both human beings and animals. Both search for me but it is hard to find me. I travel to benefit them. What am I?

A scent or smell. A scent is important to both humans and animals and both search for scents (for different reasons). A scent travels through the air to benefit humans and animals, again, for different reasons.

Special thanks to Vavessa for the answer to this one.

Posted in Riddles

Three Two Three Sequence

What number belongs at the beginning of this sequence?

?, 3, 2, 3, 9, 2, 4, 8, 4, 3, 7, 6

3 ½.

If you break up the numbers into groups of 4, a,b,c,d, then 2 × |a – d| = |b – c|.

9 2 4 8 → 2 × |9 – 8| = |2 – 4|, or 2 × 1 = 2
4 3 7 6 → 2 × |4 – 6| = |3 – 7|, or 2 × 2 = 4, so
n 3 2 3 → 2 × |3 ½ – 3| = |3 – 2|, or 2 × ½ = 1;

I’m not sure this is the correct solution, but it’s the best I’ve found so far. Email me if you know of a better one.

Posted in Brain Teasers
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Can’t Keep It Until You’ve Given It

You can’t keep this until you have given it.

A promise (or your word).

Posted in Riddles

One Three Five

What word comes next?

one three five four ______

Four. Each word is the number of letters in the previous word. And since four has four letters, it would continue with four forever after.

Posted in Brain Teasers

Swallow

You can swallow me, but I can swallow you. What am I?

Water.

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If You Break Me, I Don’t Stop Working

If you break me
I do not stop working,
If you touch me
I may be snared,
If you lose me
Nothing will matter.

Your heart.

Posted in Riddles

How Old is Lilly?

Two days ago Lilly was 7 years old. Next year she will turn 10. How can this be?

Her birthday is December 31st. Today is January 1st so she was 7 two days ago, and turned 7 last year. Now she’s 8 and will turn 9 this year. And next year she’ll turn 10.

For example, if today is 01 Jan 2015:

30 Dec 2014 = age 7 (two days ago)
01 Jan 2015 = age 8 (today, she turned 8 on 31 Dec 2014, which was last year)
31 Dec 2015 = age 9 (her birthday this year)
31 Dec 2016 = age 10 (her birthday next year)

Posted in Brain Teasers

Priscilla and Bruce Exchanging Money

Priscilla gave her brother Bruce as much money as Bruce started with. Bruce gave Priscilla as much money as Priscilla had left. Priscilla then gave Bruce as much as Bruce had left, which left Priscilla broke. Bruce had $80.00.

How much money did Priscilla and Bruce start with?

Priscilla: $50
Bruce: $30

Step 1
Priscilla gives Bruce $30
Priscilla: $20
Bruce: $60

Step 2
Bruce gives Priscilla $20
Priscilla: $40
Bruce: $40

Step 3
Priscilla gives Bruce $40
Priscilla: $0
Bruce: $80

Posted in Brain Teasers