The conditional distribution of one random variable X given an observed value y of another random variable Y is the distribution we would use for X if we were to learn that Y=y. when dealing with the conditional distribution of X given Y=y, it is safe to behave as if Y were the constant y. If X and Y have joint p.f.,p.d.f., or p.f./p.d.f. f(x,y) then the conditionalp.f. or p.d.f. of X given Y=y is g_1 (x│y)=f(x,y)/f_2 (y), where f_2is the marginal p.f. or p.d.f. of Y . when it is convenient to specify a conditional distribution directly, the joint distribution can be constructed from the conditional together with the other marginal. For example,