Mixed Animals for $100

At the market you can buy a cow for $10, a pig for $1 and 8 hens for $1. How many animals would you need to buy to get 100 mixed animals for exactly $100?

7 cows, 21 pigs and 72 hens. The trick to this is finding the combination of cows and hens with the same cost and quantity since pigs are already equal. The magic combination is 7 cows and 72 hens, giving you 79 animals that cost $79 ($70 + $9). Then you just add 21 pigs to get to 100 animals.

Posted in Brain Teasers

What Has Four Legs and Flies?

What has four legs and flies?

A horse with bugs or two pairs of trousers. The four legs should be obvious and the flies are the zippers.

Posted in Riddles

Find The Country Names

How many country names can you find in the following statements?

Don’t reach in a crack in the rocks, there might be snakes in there.
While I was on the highway called the Alcan, a daily occurrence was car breakdowns.
The top social class, as defined by many, is the upper-upper.

Three.

1. China (reaCH IN A)
2. Canada (alCAN A DAily)
3. Peru (upPER-Upper)

Posted in Brain Teasers

Messy Math

What is the answer to this problem?

48 / 2(9 + 3) = ?

It depends. Usually, math has one right answer, but in this case, the order of operations can get a little quirky.

There are two ways to solve this. First, like so:
48 / 2 × (9 + 3) = ?
48 / 2 × (12) = ?
24 × 12 = 288

But another, arguably valid way is:
48 / 2 × (9 + 3) = ?
48 / 2 × (12) = ?
48 / 24 = 2

Thanks to KnowYourMeme for providing a great overview on this one. Math StackExchange has more discussion.

Posted in Brain Teasers

Five Games of Checkers

Two children were playing checkers and each played five games. Both children won the same number of games yet there were no ties. How is this possible?

They weren’t playing each other.

Posted in Brain Teasers

The Ages of a Prince and Princess

A princess is as old as the prince will be when the princess is twice the age that the prince was when the princess’s age was half the sum of their present ages.

What are their ages?

This one took a while to figure out and there are numerous valid ways of finding the answer.

Here is the solution I came up with

I created the following table from the riddle:

  Current Future Past
Princess x 2z (x+y)/2
Prince y x z

I then created three equations, since the difference in their age will always be the same.
d = the difference in ages
x – y = d
2z – x = d
x/2 + y/2 – z = d

I then created a matrix and solved it using row reduction.

x y z
1 -1 0 d
-1 0 2 d
.5 .5 -1 d

It reduced to:

x y z
1 0 0 4d
0 1 0 3d
0 0 1 5d/2

This means that you can pick any difference you want (an even one presumably because you want integer ages).
Princess age: 4d
Prince age: 3d

Ages that work

Princess Prince
4 3
8 6
16 12
24 18
32 24
40 30
48 36
56 42
64 48
72 54
80 60

To see other solutions check out the comments from when I posted this on my blog.

Posted in Brain Teasers

A Hidden Message

44 33 555 555 666 9 666 777 555 3

What is the message in this code?

Pressing these digits in sequence will produce HELLO WORLD on a cell phone (for an SMS text message).

Posted in Brain Teasers

A Woman Shoots Her Husband

A woman shoots her husband, then holds him under water for five minutes. Finally, she hangs him. Five minutes later they enjoy a wonderful dinner together. How can this be?

She took a photo of him and developed it in the dark room.

Posted in Riddles

Jump Dog Jump

A man says his dog can jump over his house. No one believes him but he is right. How is that possible?

The dog can jump over his dog house.

Posted in Brain Teasers

I Know of Word of Letters Three

I know a word of letters three. Add two, and fewer there will be

Few.

Posted in Riddles