Why is Friday 13th unlucky?

I have always wonderd why Friday the 13th is unlucky. Most people say that Friday the 13th is the unluckyest day out of the whole year!

No one is certain what the exact origin of the superstition is but the number 13 and Friday both have a long history of bringing bad luck and its the combanation of both days together that makes it the most feared of all.

''Unlucky 13''
Some people think that the number 13 is bad luck because of the bible. Judas, who betrayed Jesus, is thought to have been the 13th guest to sit down to the Last Supper.

Even today, people will not allow 13 people at their dinner table. If they want 13 guests they place a teddy bear in a seat to make it 14.

Others such as hotel managers think that it's not right to have a room number named after 13 or a 13th floor, they skip right to 14 and 15.

''Unlucky Friday''
Friday has always been considered as the worst day of the week.
For Example:
In Britain, Friday was once known as Hangman's Day because it was usually when people who had been condemned to death would be hanged.
Good Friday - the day of Jesus Christ's crucifixion is known to be the only good and lucky Friday.

So both of these put together = Unluky Friday the 13th.