Most of my friends are extroverts, but I'm an introvert
Those terms were popularized by Carl Jung,
How long ago?
Not sure, but they are typically viewed on a single contiuum.
Is there typically a 50/50 split between the two?
Extraversion and introversion
The trait of extraversion–introversion is a central dimension of human personality theories. The terms "introversion" and "extraversion" were popularized by Carl Jung, although both the popular understanding and psychological usage differ from his original intent. Extraversion tends to be manifested in outgoing, talkative, energetic behavior, whereas introversion is manifested in more reserved and solitary behavior. Virtually all comprehensive models of personality include these concepts in various forms. Examples include the Big Five model, Jung's analytical psychology, Hans Eysenck's
four weeks long break during winter (typically starting on 31 December). School is not out on Christmas or Easter, but students who celebrate those holidays are allowed to miss that day of school.
By country Brazil.
In Brazil, summer break lasts between 50 and 60 days; from late November - early December, to early February. In addition, for the majority of Brazilian students there are two to three weeks off for winter in July; the winter holidays were held in August for 2016 only due to the