so say 15% of people are in the x category for each opposition. that means the chances of XXXX are .15^4 (since the variables are independent of each other).
edit: even if you assume 33% or 50% likelihood in each dichotomy, you still have to multiply the chances of each one.
33% for one letter --> .33^4 chance of XXXX
50% for one letter --> .5^4 chance of XXXX