There are 5 houses in 5 different colors. In each house lives a person with a different nationality. The 5 owners drink a certain type of beverage, smoke a certain brand of cigar, and keep a certain pet. No owners have the same pet, smoke the same brand of cigar, or drink the same beverage.

Somebody owns a fish. The question is: who?

Hints:

• The Brit lives in the red house.
• The Swede keeps dogs as pets.
• The Dane drinks tea.
• The green house is on the left and next to the white house.
• The green homeowner drinks coffee.
• The person who smokes Pall Mall rears birds.
• The owner of the yellow house smokes Dunhill.
• The man living in the center house drinks milk.
• The Norwegian lives in the first house.
• The man who smokes Blends lives next to the one who keeps cats.
• The man who keeps the horse lives next to the man who smokes Dunhill.
• The owner who smokes Bluemaster drinks beer.
• The German smokes Prince.
• The Norwegian lives next to the blue house.
• The man who smokes Blends has a neighbor who drinks water.

How can you put (without using glue or something like that) ten nails on the head of a standing nail? The final construction should be stable.

A perfect number is a number which is equal to the sum of all its divisors. For example 6 is divisable by 1,2,3 and 1 + 2 + 3 = 6. Can you find another perfect number?