Many people don’t think that the number 13 is a lucky number. Many hotels do not have a 13th floor. The floors go from 12 to 14, and there is no number13. Some people will never sit at a table with 12 other people. They will tell someone to go or ask another person to sit with them.
No one really knows why people do not like the number 13. Perhaps one reason is that when people began to count, they used ten fingers and two hands. This made 12. They could not count more.
Some Christians (基督徒) say that 13 is not lucky because there were 13 people at a meal the day before Jesus (耶稣) was killed (被杀). In a story about the old Greek (希腊的) gods, 12 gods were asked to a meal but one more came. This made 13. It is why the god Balder, who was at the meal, was killed.
里填上适当的数，再列综合算式。