Hey, we just went over independence and the like in class, but i didnt quite understand how to apply the obvious idea of independent events to making formulae. Can someone help me set this problem up?

Assume identical twins are always of the same sex, equally likely boys or girls. Assume that for fraternal twins the firstborn is equally likely to be a boy or a girl, and so is the secondborn, independently of the first Assume that proportion p of twins are identical, and proportion q = 1 - p are fraternal. Find formulae in terms of p for the following probabilities for twins:

a) P(both boys)
b) P(firstborn boy and secondborn girl)
etc etc...

Some help setting this up would be appreciated.