False, false, false.
Here are some of the reasons why:
1) 28 days is the average length of a menstrual cycle, but most women actually don't have 28-day cycles.
So any assumptions based on a 28-day cycle won't be true for most women anyway.
2) Ovulation usually occurs about 12-14 days from the end of a cycle, that's true.
But you can only work it out by counting backwards (i.e. when you start your period, you can then count back and work out roughly when you might have ovulated). Especially in young women, the timing of ovulation can vary a lot, and you may even ovulate more than once in a cycle.
So unless you are charting your basal body temperature and monitoring your cervical mucus daily, you don't have the info to even try to predict when you will ovulate.
3) Once an egg has been released, its "shelf-life" is about 48 hours max. But sperm can survive in a friendly environment like the vagina for up to a week, hanging around waiting for that egg to be released.
In practice, what this means is that you can get pregnant on pretty much any day of your cycle.
There aren't any "safe days".
[This message has been edited by logic_grrl (edited 03-22-2004).]